| Message ID | 20210123034655.102813-1-john.stultz@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2,1/3] dma-buf: heaps: Add deferred-free-helper library code | expand |
On Fri, Jan 22, 2021 at 7:47 PM John Stultz <john.stultz@linaro.org> wrote: > +static int system_heap_clear_pages(struct page **pages, int num, pgprot_t pgprot) > +{ > + void *addr = vmap(pages, num, VM_MAP, pgprot); > + > + if (!addr) > + return -ENOMEM; > + memset(addr, 0, PAGE_SIZE * num); > + vunmap(addr); > + return 0; > +} I thought that vmap/vunmap are expensive, and I am wondering if there's a faster way that avoids vmap. How about lifting this code from lib/iov_iter.c static void memzero_page(struct page *page, size_t offset, size_t len) { char *addr = kmap_atomic(page); memset(addr + offset, 0, len); kunmap_atomic(addr); } Or what about lifting that code from the old ion_cma_heap.c if (PageHighMem(pages)) { unsigned long nr_clear_pages = nr_pages; struct page *page = pages; while (nr_clear_pages > 0) { void *vaddr = kmap_atomic(page); memset(vaddr, 0, PAGE_SIZE); kunmap_atomic(vaddr); page++; nr_clear_pages--; } } else { memset(page_address(pages), 0, size); }
On Wed, Jan 27, 2021 at 12:21 PM Daniel Mentz <danielmentz@google.com> wrote: > > On Fri, Jan 22, 2021 at 7:47 PM John Stultz <john.stultz@linaro.org> wrote: > > +static int system_heap_clear_pages(struct page **pages, int num, pgprot_t pgprot) > > +{ > > + void *addr = vmap(pages, num, VM_MAP, pgprot); > > + > > + if (!addr) > > + return -ENOMEM; > > + memset(addr, 0, PAGE_SIZE * num); > > + vunmap(addr); > > + return 0; > > +} > > I thought that vmap/vunmap are expensive, and I am wondering if > there's a faster way that avoids vmap. > > How about lifting this code from lib/iov_iter.c > static void memzero_page(struct page *page, size_t offset, size_t len) > { > char *addr = kmap_atomic(page); > memset(addr + offset, 0, len); > kunmap_atomic(addr); > } > > Or what about lifting that code from the old ion_cma_heap.c > > if (PageHighMem(pages)) { > unsigned long nr_clear_pages = nr_pages; > struct page *page = pages; > > while (nr_clear_pages > 0) { > void *vaddr = kmap_atomic(page); > > memset(vaddr, 0, PAGE_SIZE); > kunmap_atomic(vaddr); > page++; > nr_clear_pages--; > } > } else { > memset(page_address(pages), 0, size); > } Though, this last memset only works since CMA is contiguous, so it probably needs to always do the kmap_atomic for each page, right? I'm still a little worried if this is right, as the current implementation with the vmap comes from the old ion_heap_sglist_zero logic, which similarly tries to batch the vmaps 32 pages at at time, but I'll give it a try. thanks -john
On Wed, Jan 27, 2021 at 9:10 PM John Stultz <john.stultz@linaro.org> wrote: > > On Wed, Jan 27, 2021 at 12:21 PM Daniel Mentz <danielmentz@google.com> wrote: > > > > On Fri, Jan 22, 2021 at 7:47 PM John Stultz <john.stultz@linaro.org> wrote: > > > +static int system_heap_clear_pages(struct page **pages, int num, pgprot_t pgprot) > > > +{ > > > + void *addr = vmap(pages, num, VM_MAP, pgprot); > > > + > > > + if (!addr) > > > + return -ENOMEM; > > > + memset(addr, 0, PAGE_SIZE * num); > > > + vunmap(addr); > > > + return 0; > > > +} > > > > I thought that vmap/vunmap are expensive, and I am wondering if > > there's a faster way that avoids vmap. > > > > How about lifting this code from lib/iov_iter.c > > static void memzero_page(struct page *page, size_t offset, size_t len) > > { > > char *addr = kmap_atomic(page); > > memset(addr + offset, 0, len); > > kunmap_atomic(addr); > > } > > > > Or what about lifting that code from the old ion_cma_heap.c > > > > if (PageHighMem(pages)) { > > unsigned long nr_clear_pages = nr_pages; > > struct page *page = pages; > > > > while (nr_clear_pages > 0) { > > void *vaddr = kmap_atomic(page); > > > > memset(vaddr, 0, PAGE_SIZE); > > kunmap_atomic(vaddr); > > page++; > > nr_clear_pages--; > > } > > } else { > > memset(page_address(pages), 0, size); > > } > > Though, this last memset only works since CMA is contiguous, so it > probably needs to always do the kmap_atomic for each page, right? Yeah, but with the system heap page pool, some of these pages might be 64KB or 1MB large. kmap_atomic(page) just maps to page_address(page) in most cases. I think iterating over all pages individually in this manner might still be faster than using vmap. > > I'm still a little worried if this is right, as the current > implementation with the vmap comes from the old ion_heap_sglist_zero > logic, which similarly tries to batch the vmaps 32 pages at at time, > but I'll give it a try.
diff --git a/drivers/dma-buf/heaps/Kconfig b/drivers/dma-buf/heaps/Kconfig index a5eef06c4226..ecf65204f714 100644 --- a/drivers/dma-buf/heaps/Kconfig +++ b/drivers/dma-buf/heaps/Kconfig @@ -1,3 +1,6 @@ +config DMABUF_HEAPS_DEFERRED_FREE + bool + config DMABUF_HEAPS_SYSTEM bool "DMA-BUF System Heap" depends on DMABUF_HEAPS diff --git a/drivers/dma-buf/heaps/Makefile b/drivers/dma-buf/heaps/Makefile index 974467791032..4e7839875615 100644 --- a/drivers/dma-buf/heaps/Makefile +++ b/drivers/dma-buf/heaps/Makefile @@ -1,3 +1,4 @@ # SPDX-License-Identifier: GPL-2.0 +obj-$(CONFIG_DMABUF_HEAPS_DEFERRED_FREE) += deferred-free-helper.o obj-$(CONFIG_DMABUF_HEAPS_SYSTEM) += system_heap.o obj-$(CONFIG_DMABUF_HEAPS_CMA) += cma_heap.o diff --git a/drivers/dma-buf/heaps/deferred-free-helper.c b/drivers/dma-buf/heaps/deferred-free-helper.c new file mode 100644 index 000000000000..cf04148167a2 --- /dev/null +++ b/drivers/dma-buf/heaps/deferred-free-helper.c @@ -0,0 +1,136 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Deferred dmabuf freeing helper + * + * Copyright (C) 2020 Linaro, Ltd. + * + * Based on the ION page pool code + * Copyright (C) 2011 Google, Inc. + */ + +#include <linux/freezer.h> +#include <linux/list.h> +#include <linux/slab.h> +#include <linux/swap.h> +#include <linux/sched/signal.h> + +#include "deferred-free-helper.h" + +static LIST_HEAD(free_list); +static size_t list_size; +wait_queue_head_t freelist_waitqueue; +struct task_struct *freelist_task; +static DEFINE_SPINLOCK(free_list_lock); + +void deferred_free(struct deferred_freelist_item *item, + void (*free)(struct deferred_freelist_item*, + enum df_reason), + size_t size) +{ + unsigned long flags; + + INIT_LIST_HEAD(&item->list); + item->size = size; + item->free = free; + + spin_lock_irqsave(&free_list_lock, flags); + list_add(&item->list, &free_list); + list_size += size; + spin_unlock_irqrestore(&free_list_lock, flags); + wake_up(&freelist_waitqueue); +} + +static size_t free_one_item(enum df_reason reason) +{ + unsigned long flags; + size_t size = 0; + struct deferred_freelist_item *item; + + spin_lock_irqsave(&free_list_lock, flags); + if (list_empty(&free_list)) { + spin_unlock_irqrestore(&free_list_lock, flags); + return 0; + } + item = list_first_entry(&free_list, struct deferred_freelist_item, list); + list_del(&item->list); + size = item->size; + list_size -= size; + spin_unlock_irqrestore(&free_list_lock, flags); + + item->free(item, reason); + return size; +} + +static unsigned long get_freelist_size(void) +{ + unsigned long size; + unsigned long flags; + + spin_lock_irqsave(&free_list_lock, flags); + size = list_size; + spin_unlock_irqrestore(&free_list_lock, flags); + return size; +} + +static unsigned long freelist_shrink_count(struct shrinker *shrinker, + struct shrink_control *sc) +{ + return get_freelist_size(); +} + +static unsigned long freelist_shrink_scan(struct shrinker *shrinker, + struct shrink_control *sc) +{ + int total_freed = 0; + + if (sc->nr_to_scan == 0) + return 0; + + while (total_freed < sc->nr_to_scan) { + int freed = free_one_item(DF_UNDER_PRESSURE); + + if (!freed) + break; + + total_freed += freed; + } + + return total_freed; +} + +static struct shrinker freelist_shrinker = { + .count_objects = freelist_shrink_count, + .scan_objects = freelist_shrink_scan, + .seeks = DEFAULT_SEEKS, + .batch = 0, +}; + +static int deferred_free_thread(void *data) +{ + while (true) { + wait_event_freezable(freelist_waitqueue, + get_freelist_size() > 0); + + free_one_item(DF_NORMAL); + } + + return 0; +} + +static int deferred_freelist_init(void) +{ + list_size = 0; + + init_waitqueue_head(&freelist_waitqueue); + freelist_task = kthread_run(deferred_free_thread, NULL, + "%s", "dmabuf-deferred-free-worker"); + if (IS_ERR(freelist_task)) { + pr_err("%s: creating thread for deferred free failed\n", + __func__); + return -1; + } + sched_set_normal(freelist_task, 19); + + return register_shrinker(&freelist_shrinker); +} +device_initcall(deferred_freelist_init); diff --git a/drivers/dma-buf/heaps/deferred-free-helper.h b/drivers/dma-buf/heaps/deferred-free-helper.h new file mode 100644 index 000000000000..2c43dd5a3eda --- /dev/null +++ b/drivers/dma-buf/heaps/deferred-free-helper.h @@ -0,0 +1,55 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef DEFERRED_FREE_HELPER_H +#define DEFERRED_FREE_HELPER_H + +/** + * df_reason - enum for reason why item was freed + * + * This provides a reason for why the free funciton was called + * on the item. This is useful when deferred_free is used in + * combination with a pagepool, so under pressure the page can + * be immediately freed. + * + * DF_NORMAL: Normal deferred free + * + * DF_UNDER_PRESSURE: Free was called because the system + * is under memory pressure. Usually + * from a shrinker. Avoid allocating + * memory in the free call, as it may + * fail. + */ +enum df_reason { + DF_NORMAL, + DF_UNDER_PRESSURE, +}; + +/** + * deferred_freelist_item - item structure for deferred freelist + * + * This is to be added to the structure for whatever you want to + * defer freeing on. + * + * @size: size of the item to be freed + * @free: function pointer to be called when freeing the item + * @list: list entry for the deferred list + */ +struct deferred_freelist_item { + size_t size; + void (*free)(struct deferred_freelist_item *i, + enum df_reason reason); + struct list_head list; +}; + +/** + * deferred_free - call to add item to the deferred free list + * + * @item: Pointer to deferred_freelist_item field of a structure + * @free: Function pointer to the free call + * @size: Size of the item to be freed + */ +void deferred_free(struct deferred_freelist_item *item, + void (*free)(struct deferred_freelist_item *i, + enum df_reason reason), + size_t size); +#endif
This patch provides infrastructure for deferring buffer frees. This is a feature ION provided which when used with some form of a page pool, provides a nice performance boost in an allocation microbenchmark. The reason it helps is it allows the page-zeroing to be done out of the normal allocation/free path, and pushed off to a kthread. As not all heaps will find this useful, its implemented as a optional helper library that heaps can utilize. Cc: Daniel Vetter <daniel@ffwll.ch> Cc: Sumit Semwal <sumit.semwal@linaro.org> Cc: Liam Mark <lmark@codeaurora.org> Cc: Chris Goldsworthy <cgoldswo@codeaurora.org> Cc: Laura Abbott <labbott@kernel.org> Cc: Brian Starkey <Brian.Starkey@arm.com> Cc: Hridya Valsaraju <hridya@google.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Sandeep Patil <sspatil@google.com> Cc: Daniel Mentz <danielmentz@google.com> Cc: Ørjan Eide <orjan.eide@arm.com> Cc: Robin Murphy <robin.murphy@arm.com> Cc: Ezequiel Garcia <ezequiel@collabora.com> Cc: Simon Ser <contact@emersion.fr> Cc: James Jones <jajones@nvidia.com> Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Signed-off-by: John Stultz <john.stultz@linaro.org> --- v2: * Fix sleep in atomic issue from using a mutex, by switching to a spinlock as Reported-by: kernel test robot <oliver.sang@intel.com> * Cleanup API to use a reason enum for clarity and add some documentation comments as suggested by Suren Baghdasaryan. --- drivers/dma-buf/heaps/Kconfig | 3 + drivers/dma-buf/heaps/Makefile | 1 + drivers/dma-buf/heaps/deferred-free-helper.c | 136 +++++++++++++++++++ drivers/dma-buf/heaps/deferred-free-helper.h | 55 ++++++++ 4 files changed, 195 insertions(+) create mode 100644 drivers/dma-buf/heaps/deferred-free-helper.c create mode 100644 drivers/dma-buf/heaps/deferred-free-helper.h