| Message ID | 20230727093637.1262110-1-usama.anjum@collabora.com |
|---|---|
| Headers | show |
| Series | Implement IOCTL to get and optionally clear info about PTEs | expand |
On Fri, Jul 28, 2023 at 04:02:02PM +0500, Muhammad Usama Anjum wrote: > We are optimizing for more performance. Please find the change-set below > for easy review before next revision and post your comments: > > - Replace memcpy() with direct copy as it proving to be very expensive > - Don't check if PAGE_IS_FILE if no mask needs it as it is very > expensive to check per pte > - Add question in comment for discussion purpose > - Add fast path for exclusive WP for ptes Please read the kernel documentation for how to properly submit patches (i.e. don't mush them all together into one and then properly describe what you are doing and why you are doing it). Also actually test the patch and prove (or disprove) if it does matter for performance. good luck! greg k-h
On Thu, Jul 27, 2023 at 02:36:34PM +0500, Muhammad Usama Anjum wrote: <snip> > + > +static void pagemap_scan_backout_range(struct pagemap_scan_private *p, > + unsigned long addr, unsigned long end, > + unsigned long end_addr) It hard to figure out what difference between end and end_addr. I would add a comment here. > +{ > + struct page_region *cur_buf = &p->cur_buf; > + > + if (cur_buf->start != addr) > + cur_buf->end = addr; > + else > + cur_buf->start = cur_buf->end = 0; > + > + p->end_addr = end_addr; > + p->found_pages -= (end - addr) / PAGE_SIZE; > +} > + > +static int pagemap_scan_output(unsigned long categories, > + struct pagemap_scan_private *p, > + unsigned long addr, unsigned long *end) > +{ > + unsigned long n_pages, total_pages; > + int ret = 0; > + > + if (!pagemap_scan_is_interesting_page(categories, p)) { > + *end = addr; > + return 0; > + } > + > + if (!p->vec_buf) > + return 0; > + > + categories &= p->arg.return_mask; > + > + n_pages = (*end - addr) / PAGE_SIZE; > + if (check_add_overflow(p->found_pages, n_pages, &total_pages) || > + total_pages > p->arg.max_pages) { why do we need to use check_add_overflow here? > + size_t n_too_much = total_pages - p->arg.max_pages; it is unsafe to use total_pages if check_add_overflow returns non-zero. > + *end -= n_too_much * PAGE_SIZE; > + n_pages -= n_too_much; > + ret = -ENOSPC; > + } > + > + if (!pagemap_scan_push_range(categories, p, addr, *end)) { > + *end = addr; > + n_pages = 0; > + ret = -ENOSPC; > + } > + > + p->found_pages += n_pages; > + if (ret) > + p->end_addr = *end; > + > + return ret; > +} > + > +static int pagemap_scan_thp_entry(pmd_t *pmd, unsigned long start, > + unsigned long end, struct mm_walk *walk) > +{ > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > + struct pagemap_scan_private *p = walk->private; > + struct vm_area_struct *vma = walk->vma; > + unsigned long categories; > + spinlock_t *ptl; > + int ret = 0; > + > + ptl = pmd_trans_huge_lock(pmd, vma); > + if (!ptl) > + return -ENOENT; > + > + categories = p->cur_vma_category | pagemap_thp_category(*pmd); > + > + ret = pagemap_scan_output(categories, p, start, &end); > + if (start == end) > + goto out_unlock; > + > + if (~p->arg.flags & PM_SCAN_WP_MATCHING) > + goto out_unlock; > + if (~categories & PAGE_IS_WRITTEN) > + goto out_unlock; > + > + /* > + * Break huge page into small pages if the WP operation > + * need to be performed is on a portion of the huge page. > + */ > + if (end != start + HPAGE_SIZE) { > + spin_unlock(ptl); > + split_huge_pmd(vma, pmd, start); > + pagemap_scan_backout_range(p, start, end, 0); pagemap_scan_backout_range looks "weird"... imho, it makes the code harder for understanding. > + return -ENOENT; I think you need to add a comment that this ENOENT is a special case. > + } > + > + make_uffd_wp_pmd(vma, start, pmd); > + flush_tlb_range(vma, start, end); > +out_unlock: > + spin_unlock(ptl); > + return ret; > +#else /* !CONFIG_TRANSPARENT_HUGEPAGE */ > + return -ENOENT; > +#endif > +} > + > +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, > + unsigned long end, struct mm_walk *walk) > +{ > + struct pagemap_scan_private *p = walk->private; > + struct vm_area_struct *vma = walk->vma; > + pte_t *pte, *start_pte; > + unsigned long addr; > + bool flush = false; > + spinlock_t *ptl; > + int ret; > + > + arch_enter_lazy_mmu_mode(); > + > + ret = pagemap_scan_thp_entry(pmd, start, end, walk); > + if (ret != -ENOENT) { > + arch_leave_lazy_mmu_mode(); > + return ret; > + } > + > + start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl); > + if (!pte) { > + arch_leave_lazy_mmu_mode(); > + walk->action = ACTION_AGAIN; > + return 0; > + } > + > + for (addr = start; addr != end; pte++, addr += PAGE_SIZE) { > + unsigned long categories = p->cur_vma_category | > + pagemap_page_category(vma, addr, ptep_get(pte)); > + unsigned long next = addr + PAGE_SIZE; > + > + ret = pagemap_scan_output(categories, p, addr, &next); > + if (next == addr) { > + if (!ret) > + continue; > + break; > + } > + > + if (~p->arg.flags & PM_SCAN_WP_MATCHING) > + continue; > + if (~categories & PAGE_IS_WRITTEN) > + continue; > + > + make_uffd_wp_pte(vma, addr, pte); > + if (!flush) { > + start = addr; > + flush = true; > + } > + } > + > + if (flush) > + flush_tlb_range(vma, start, addr); > + > + pte_unmap_unlock(start_pte, ptl); > + arch_leave_lazy_mmu_mode(); > + > + cond_resched(); > + return ret; > +} > + > +#ifdef CONFIG_HUGETLB_PAGE > +static int pagemap_scan_hugetlb_entry(pte_t *ptep, unsigned long hmask, > + unsigned long start, unsigned long end, > + struct mm_walk *walk) > +{ > + struct pagemap_scan_private *p = walk->private; > + struct vm_area_struct *vma = walk->vma; > + unsigned long categories; > + spinlock_t *ptl; > + int ret = 0; > + pte_t pte; > + > + if (~p->arg.flags & PM_SCAN_WP_MATCHING) { > + /* Go the short route when not write-protecting pages. */ > + > + pte = huge_ptep_get(ptep); > + categories = p->cur_vma_category | pagemap_hugetlb_category(pte); > + > + return pagemap_scan_output(categories, p, start, &end); > + } > + > + i_mmap_lock_write(vma->vm_file->f_mapping); > + ptl = huge_pte_lock(hstate_vma(vma), vma->vm_mm, ptep); > + > + pte = huge_ptep_get(ptep); > + categories = p->cur_vma_category | pagemap_hugetlb_category(pte); > + > + ret = pagemap_scan_output(categories, p, start, &end); > + if (start == end) > + goto out_unlock; > + > + if (~categories & PAGE_IS_WRITTEN) > + goto out_unlock; > + > + if (end != start + HPAGE_SIZE) { > + /* Partial HugeTLB page WP isn't possible. */ > + pagemap_scan_backout_range(p, start, end, start); > + ret = -EINVAL; Why is it EINVAL in this case? > + goto out_unlock; > + } > + > + make_uffd_wp_huge_pte(vma, start, ptep, pte); > + flush_hugetlb_tlb_range(vma, start, end); > + > +out_unlock: > + spin_unlock(ptl); > + i_mmap_unlock_write(vma->vm_file->f_mapping); > + > + return ret; > +} > +#else > +#define pagemap_scan_hugetlb_entry NULL > +#endif > + > +static int pagemap_scan_pte_hole(unsigned long addr, unsigned long end, > + int depth, struct mm_walk *walk) > +{ > + struct pagemap_scan_private *p = walk->private; > + struct vm_area_struct *vma = walk->vma; > + int ret, err; > + > + if (!vma) > + return 0; > + > + ret = pagemap_scan_output(p->cur_vma_category, p, addr, &end); > + if (addr == end) > + return ret; > + > + if (~p->arg.flags & PM_SCAN_WP_MATCHING) > + return ret; > + > + err = uffd_wp_range(vma, addr, end - addr, true); > + if (err < 0) > + ret = err; > + > + return ret; > +} > + > +static const struct mm_walk_ops pagemap_scan_ops = { > + .test_walk = pagemap_scan_test_walk, > + .pmd_entry = pagemap_scan_pmd_entry, > + .pte_hole = pagemap_scan_pte_hole, > + .hugetlb_entry = pagemap_scan_hugetlb_entry, > +}; > + > +static int pagemap_scan_get_args(struct pm_scan_arg *arg, > + unsigned long uarg) > +{ > + if (copy_from_user(arg, (void __user *)uarg, sizeof(*arg))) > + return -EFAULT; > + > + if (arg->size != sizeof(struct pm_scan_arg)) > + return -EINVAL; > + > + /* Validate requested features */ > + if (arg->flags & ~PM_SCAN_FLAGS) > + return -EINVAL; > + if ((arg->category_inverted | arg->category_mask | > + arg->category_anyof_mask | arg->return_mask) & ~PM_SCAN_CATEGORIES) > + return -EINVAL; > + > + arg->start = untagged_addr((unsigned long)arg->start); > + arg->end = untagged_addr((unsigned long)arg->end); > + arg->vec = untagged_addr((unsigned long)arg->vec); > + > + /* Validate memory pointers */ > + if (!IS_ALIGNED(arg->start, PAGE_SIZE)) > + return -EINVAL; > + if (!access_ok((void __user *)arg->start, arg->end - arg->start)) > + return -EFAULT; > + if (!arg->vec && arg->vec_len) > + return -EFAULT; > + if (arg->vec && !access_ok((void __user *)arg->vec, > + arg->vec_len * sizeof(struct page_region))) > + return -EFAULT; > + > + /* Fixup default values */ > + arg->end = ALIGN(arg->end, PAGE_SIZE); > + if (!arg->max_pages) > + arg->max_pages = ULONG_MAX; > + > + return 0; > +} > + > +static int pagemap_scan_writeback_args(struct pm_scan_arg *arg, > + unsigned long uargl) > +{ > + struct pm_scan_arg __user *uarg = (void __user *)uargl; > + > + if (copy_to_user(&uarg->walk_end, &arg->walk_end, sizeof(arg->walk_end))) > + return -EFAULT; > + > + return 0; > +} > + > +static int pagemap_scan_init_bounce_buffer(struct pagemap_scan_private *p) > +{ > + if (!p->arg.vec_len) { > + /* > + * An arbitrary non-page-aligned sentinel value for > + * pagemap_scan_push_range(). > + */ > + p->cur_buf.start = p->cur_buf.end = ULLONG_MAX; > + if (p->arg.vec) > + p->vec_buf = ZERO_SIZE_PTR; > + return 0; > + } > + > + /* > + * Allocate a smaller buffer to get output from inside the page > + * walk functions and walk the range in PAGEMAP_WALK_SIZE chunks. > + * The last range is always stored in p.cur_buf to allow coalescing > + * consecutive ranges that have the same categories returned across > + * walk_page_range() calls. > + */ > + p->vec_buf_len = min_t(size_t, PAGEMAP_WALK_SIZE >> PAGE_SHIFT, > + p->arg.vec_len - 1); > + p->vec_buf = kmalloc_array(p->vec_buf_len, sizeof(*p->vec_buf), > + GFP_KERNEL); > + if (!p->vec_buf) > + return -ENOMEM; > + > + p->vec_out = (struct page_region __user *)p->arg.vec; > + > + return 0; > +} > + > +static int pagemap_scan_flush_buffer(struct pagemap_scan_private *p) > +{ > + const struct page_region *buf = p->vec_buf; > + int n = (int)p->vec_buf_index; > + > + if (!n) > + return 0; > + > + if (copy_to_user(p->vec_out, buf, n * sizeof(*buf))) > + return -EFAULT; > + > + p->arg.vec_len -= n; > + p->vec_out += n; > + > + p->vec_buf_index = 0; > + p->vec_buf_len = min_t(size_t, p->vec_buf_len, p->arg.vec_len - 1); > + > + return n; > +} > + > +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg) > +{ > + unsigned long walk_start, walk_end; > + struct mmu_notifier_range range; > + struct pagemap_scan_private p; > + size_t n_ranges_out = 0; > + int ret; > + > + memset(&p, 0, sizeof(p)); > + ret = pagemap_scan_get_args(&p.arg, uarg); > + if (ret) > + return ret; > + > + ret = pagemap_scan_init_bounce_buffer(&p); > + if (ret) > + return ret; > + > + /* Protection change for the range is going to happen. */ > + if (p.arg.flags & PM_SCAN_WP_MATCHING) { > + mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0, > + mm, p.arg.start, p.arg.end); > + mmu_notifier_invalidate_range_start(&range); > + } > + > + walk_start = walk_end = p.arg.start; > + for (; walk_end != p.arg.end; walk_start = walk_end) { > + int n_out; > + > + walk_end = min_t(unsigned long, > + (walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK, > + p.arg.end); > + if (fatal_signal_pending(current)) { ret = EINTR; break; } > + ret = mmap_read_lock_killable(mm); > + if (ret) > + break; > + ret = walk_page_range(mm, walk_start, walk_end, > + &pagemap_scan_ops, &p); > + mmap_read_unlock(mm); > + > + n_out = pagemap_scan_flush_buffer(&p); > + if (n_out < 0) > + ret = n_out; > + else > + n_ranges_out += n_out; > + > + if (ret) > + break; > + } > + > + if (p.cur_buf.start != p.cur_buf.end) { > + if (copy_to_user(p.vec_out, &p.cur_buf, sizeof(p.cur_buf))) > + ret = -EFAULT; > + else > + ++n_ranges_out; > + } > + > + /* ENOSPC signifies early stop (buffer full) from the walk. */ > + if (!ret || ret == -ENOSPC) > + ret = n_ranges_out; > + > + p.arg.walk_end = p.end_addr ? p.end_addr : walk_start; > + if (pagemap_scan_writeback_args(&p.arg, uarg)) > + ret = -EFAULT; > + > + if (p.arg.flags & PM_SCAN_WP_MATCHING) > + mmu_notifier_invalidate_range_end(&range); > + > + kfree(p.vec_buf); > + return ret; > +} > + > +static long do_pagemap_cmd(struct file *file, unsigned int cmd, > + unsigned long arg) > +{ > + struct mm_struct *mm = file->private_data; > + > + switch (cmd) { > + case PAGEMAP_SCAN: > + return do_pagemap_scan(mm, arg); > + > + default: > + return -EINVAL; > + } > +} > + > const struct file_operations proc_pagemap_operations = { > .llseek = mem_lseek, /* borrow this */ > .read = pagemap_read, > .open = pagemap_open, > .release = pagemap_release, > + .unlocked_ioctl = do_pagemap_cmd, > + .compat_ioctl = do_pagemap_cmd, > }; > #endif /* CONFIG_PROC_PAGE_MONITOR */ > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index 0a393bc02f25b..8f8ff07453f22 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -259,6 +259,7 @@ long hugetlb_change_protection(struct vm_area_struct *vma, > unsigned long cp_flags); > > bool is_hugetlb_entry_migration(pte_t pte); > +bool is_hugetlb_entry_hwpoisoned(pte_t pte); > void hugetlb_unshare_all_pmds(struct vm_area_struct *vma); > > #else /* !CONFIG_HUGETLB_PAGE */ > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h > index b7b56871029c5..1bb3c625c2381 100644 > --- a/include/uapi/linux/fs.h > +++ b/include/uapi/linux/fs.h > @@ -305,4 +305,62 @@ typedef int __bitwise __kernel_rwf_t; > #define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\ > RWF_APPEND) > > +/* Pagemap ioctl */ > +#define PAGEMAP_SCAN _IOWR('f', 16, struct pm_scan_arg) > + > +/* Bits are set in flags of the page_region and masks in pm_scan_args */ > +#define PAGE_IS_WPALLOWED (1 << 0) > +#define PAGE_IS_WRITTEN (1 << 1) > +#define PAGE_IS_FILE (1 << 2) > +#define PAGE_IS_PRESENT (1 << 3) > +#define PAGE_IS_SWAPPED (1 << 4) > +#define PAGE_IS_PFNZERO (1 << 5) > + > +/* > + * struct page_region - Page region with flags > + * @start: Start of the region > + * @end: End of the region (exclusive) > + * @categories: PAGE_IS_* category bitmask for the region > + */ > +struct page_region { > + __u64 start; > + __u64 end; > + __u64 categories; > +}; > + > +/* Flags for PAGEMAP_SCAN ioctl */ > +#define PM_SCAN_WP_MATCHING (1 << 0) /* Write protect the pages matched. */ > +#define PM_SCAN_CHECK_WPASYNC (1 << 1) /* Abort the scan when a non-WP-enabled page is found. */ > + > +/* > + * struct pm_scan_arg - Pagemap ioctl argument > + * @size: Size of the structure > + * @flags: Flags for the IOCTL > + * @start: Starting address of the region > + * @end: Ending address of the region > + * @walk_end: Ending address of the visited memory is returned > + * (This helps if entire range hasn't been visited) > + * @vec: Address of page_region struct array for output > + * @vec_len: Length of the page_region struct array > + * @max_pages: Optional limit for number of returned pages (0 = disabled) > + * @category_inverted: PAGE_IS_* categories which values match if 0 instead of 1 > + * @category_mask: Skip pages for which any category doesn't match > + * @category_anyof_mask: Skip pages for which no category matches > + * @return_mask: PAGE_IS_* categories that are to be reported in `page_region`s returned > + */ > +struct pm_scan_arg { > + __u64 size; > + __u64 flags; > + __u64 start; > + __u64 end; > + __u64 walk_end; > + __u64 vec; > + __u64 vec_len; > + __u64 max_pages; > + __u64 category_inverted; > + __u64 category_mask; > + __u64 category_anyof_mask; > + __u64 return_mask; > +}; > + > #endif /* _UAPI_LINUX_FS_H */ > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index a073e6ed8900b..3b07db0a4f2d9 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5008,7 +5008,7 @@ bool is_hugetlb_entry_migration(pte_t pte) > return false; > } > > -static bool is_hugetlb_entry_hwpoisoned(pte_t pte) > +bool is_hugetlb_entry_hwpoisoned(pte_t pte) > { > swp_entry_t swp; > > -- > 2.39.2 >
On Thu, Jul 27, 2023 at 2:37 AM Muhammad Usama Anjum <usama.anjum@collabora.com> wrote: > <snip> > +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg) > +{ > + unsigned long walk_start, walk_end; > + struct mmu_notifier_range range; > + struct pagemap_scan_private p; > + size_t n_ranges_out = 0; > + int ret; > + > + memset(&p, 0, sizeof(p)); > + ret = pagemap_scan_get_args(&p.arg, uarg); > + if (ret) > + return ret; > + > + ret = pagemap_scan_init_bounce_buffer(&p); > + if (ret) > + return ret; > + > + /* Protection change for the range is going to happen. */ > + if (p.arg.flags & PM_SCAN_WP_MATCHING) { > + mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0, > + mm, p.arg.start, p.arg.end); > + mmu_notifier_invalidate_range_start(&range); > + } > + > + walk_start = walk_end = p.arg.start; > + for (; walk_end != p.arg.end; walk_start = walk_end) { > + int n_out; > + > + walk_end = min_t(unsigned long, > + (walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK, > + p.arg.end); This approach has performance implications. The basic program that scans its address space takes around 20-30 seconds, but it has just a few small mappings. The first optimization that comes to mind is to remove the PAGEMAP_WALK_SIZE limit and instead halt walk_page_range when the bounce buffer is full. After draining the buffer, the walk_page_range function can be restarted. The test program and perf data can be found here: https://gist.github.com/avagin/c5a22f3c78f8cb34281602dfe9c43d10 > + > + ret = mmap_read_lock_killable(mm); > + if (ret) > + break; > + ret = walk_page_range(mm, walk_start, walk_end, > + &pagemap_scan_ops, &p); > + mmap_read_unlock(mm); > + > + n_out = pagemap_scan_flush_buffer(&p); > + if (n_out < 0) > + ret = n_out; > + else > + n_ranges_out += n_out; > + > + if (ret) > + break; > + } > + Thanks, Andrei
On Fri, Jul 28, 2023 at 4:02 AM Muhammad Usama Anjum <usama.anjum@collabora.com> wrote: > > We are optimizing for more performance. Please find the change-set below > for easy review before next revision and post your comments: > > - Replace memcpy() with direct copy as it proving to be very expensive > - Don't check if PAGE_IS_FILE if no mask needs it as it is very > expensive to check per pte > - Add question in comment for discussion purpose > - Add fast path for exclusive WP for ptes > --- > fs/proc/task_mmu.c | 54 ++++++++++++++++++++++++++++++++++++---------- > 1 file changed, 43 insertions(+), 11 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 7e92c33635cab..879baf896ed0b 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1757,37 +1757,51 @@ static int pagemap_release(struct inode *inode, > struct file *file) > PAGE_IS_HUGE) > #define PM_SCAN_FLAGS (PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC) > > +#define MASKS_OF_INTEREST(a) (a.category_inverted | a.category_mask | \ > + a.category_anyof_mask | a.return_mask) > + > struct pagemap_scan_private { > struct pm_scan_arg arg; > + unsigned long masks_of_interest; > unsigned long cur_vma_category; > struct page_region *vec_buf, cur_buf; > unsigned long vec_buf_len, vec_buf_index, found_pages, end_addr; > struct page_region __user *vec_out; > }; > > -static unsigned long pagemap_page_category(struct vm_area_struct *vma, > +static unsigned long pagemap_page_category(struct pagemap_scan_private *p, > + struct vm_area_struct *vma, > unsigned long addr, pte_t pte) > { > unsigned long categories = 0; > > if (pte_present(pte)) { > - struct page *page = vm_normal_page(vma, addr, pte); > + struct page *page; > > categories |= PAGE_IS_PRESENT; > if (!pte_uffd_wp(pte)) > categories |= PAGE_IS_WRITTEN; > - if (page && !PageAnon(page)) > - categories |= PAGE_IS_FILE; > + > + if (p->masks_of_interest & PAGE_IS_FILE) { > + page = vm_normal_page(vma, addr, pte); > + if (page && !PageAnon(page)) > + categories |= PAGE_IS_FILE; > + } > + > if (is_zero_pfn(pte_pfn(pte))) > categories |= PAGE_IS_PFNZERO; > } else if (is_swap_pte(pte)) { > - swp_entry_t swp = pte_to_swp_entry(pte); > + swp_entry_t swp; > > categories |= PAGE_IS_SWAPPED; > if (!pte_swp_uffd_wp_any(pte)) > categories |= PAGE_IS_WRITTEN; > - if (is_pfn_swap_entry(swp) && !PageAnon(pfn_swap_entry_to_page(swp))) > - categories |= PAGE_IS_FILE; > + > + if (p->masks_of_interest & PAGE_IS_FILE) { > + swp = pte_to_swp_entry(pte); > + if (is_pfn_swap_entry(swp) && !PageAnon(pfn_swap_entry_to_page(swp))) > + categories |= PAGE_IS_FILE; > + } > } > > return categories; > @@ -1957,9 +1971,7 @@ static bool pagemap_scan_push_range(unsigned long > categories, > if (p->vec_buf_index >= p->vec_buf_len) > return false; > > - memcpy(&p->vec_buf[p->vec_buf_index], cur_buf, > - sizeof(*p->vec_buf)); > - ++p->vec_buf_index; > + p->vec_buf[p->vec_buf_index++] = *cur_buf; > } > > cur_buf->start = addr; > @@ -2095,9 +2107,24 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, > unsigned long start, > return 0; > } > > + if (!p->vec_buf) { > + /* Fast path for performing exclusive WP */ > + for (addr = start; addr != end; pte++, addr += PAGE_SIZE) { > + if (pte_uffd_wp(ptep_get(pte))) > + continue; > + make_uffd_wp_pte(vma, addr, pte); > + if (!flush) { > + start = addr; > + flush = true; > + } > + } > + ret = 0; > + goto flush_and_return; > + } > + > for (addr = start; addr != end; pte++, addr += PAGE_SIZE) { > unsigned long categories = p->cur_vma_category | > - pagemap_page_category(vma, addr, ptep_get(pte)); > + pagemap_page_category(p, vma, addr, ptep_get(pte)); > unsigned long next = addr + PAGE_SIZE; > > ret = pagemap_scan_output(categories, p, addr, &next); > @@ -2119,6 +2146,7 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, > unsigned long start, > } > } > > +flush_and_return: > if (flush) > flush_tlb_range(vma, start, addr); > > @@ -2284,6 +2312,9 @@ static int pagemap_scan_init_bounce_buffer(struct > pagemap_scan_private *p) > * consecutive ranges that have the same categories returned across > * walk_page_range() calls. > */ > + // Question: Increasing the vec_buf_len increases the execution speed. > + // But it'll increase the memory needed to run the IOCTL. Can we do > something here? > + // Right now only have space for 512 entries of page_region The main problem here is that walk_page_range is executed for 512 pages. I think we need to execute it for the whole range and interrupt it when we need to drain the bounce buffer. For a trivial program that scans its address space the time is reduced from 20 seconds to 0.001 seconds. The test program and perf data are here: https://gist.github.com/avagin/c5a22f3c78f8cb34281602dfe9c43d10 > p->vec_buf_len = min_t(size_t, PAGEMAP_WALK_SIZE >> PAGE_SHIFT, > p->arg.vec_len - 1); > p->vec_buf = kmalloc_array(p->vec_buf_len, sizeof(*p->vec_buf), > @@ -2329,6 +2360,7 @@ static long do_pagemap_scan(struct mm_struct *mm, > unsigned long uarg) > if (ret) > return ret; > > + p.masks_of_interest = MASKS_OF_INTEREST(p.arg); > ret = pagemap_scan_init_bounce_buffer(&p); > if (ret) > return ret; > -- > 2.39.2 >
On 8/5/23 2:53 AM, Andrei Vagin wrote: > On Thu, Jul 27, 2023 at 2:37 AM Muhammad Usama Anjum > <usama.anjum@collabora.com> wrote: >> > > <snip> > >> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg) >> +{ >> + unsigned long walk_start, walk_end; >> + struct mmu_notifier_range range; >> + struct pagemap_scan_private p; >> + size_t n_ranges_out = 0; >> + int ret; >> + >> + memset(&p, 0, sizeof(p)); >> + ret = pagemap_scan_get_args(&p.arg, uarg); >> + if (ret) >> + return ret; >> + >> + ret = pagemap_scan_init_bounce_buffer(&p); >> + if (ret) >> + return ret; >> + >> + /* Protection change for the range is going to happen. */ >> + if (p.arg.flags & PM_SCAN_WP_MATCHING) { >> + mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0, >> + mm, p.arg.start, p.arg.end); >> + mmu_notifier_invalidate_range_start(&range); >> + } >> + >> + walk_start = walk_end = p.arg.start; >> + for (; walk_end != p.arg.end; walk_start = walk_end) { >> + int n_out; >> + >> + walk_end = min_t(unsigned long, >> + (walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK, >> + p.arg.end); > > This approach has performance implications. The basic program that scans > its address space takes around 20-30 seconds, but it has just a few > small mappings. The first optimization that comes to mind is to remove > the PAGEMAP_WALK_SIZE limit and instead halt walk_page_range when the > bounce buffer is full. After draining the buffer, the walk_page_range > function can be restarted. Yeah, I've this implemented in WIP and will be posting in next revision. > > The test program and perf data can be found here: > https://gist.github.com/avagin/c5a22f3c78f8cb34281602dfe9c43d10 > >> + >> + ret = mmap_read_lock_killable(mm); >> + if (ret) >> + break; >> + ret = walk_page_range(mm, walk_start, walk_end, >> + &pagemap_scan_ops, &p); >> + mmap_read_unlock(mm); >> + >> + n_out = pagemap_scan_flush_buffer(&p); >> + if (n_out < 0) >> + ret = n_out; >> + else >> + n_ranges_out += n_out; >> + >> + if (ret) >> + break; >> + } >> + > > Thanks, > Andrei