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This is caused by CMA now supports cocurrent allocation since commit a4efc174b382 ("mm/cma.c: remove redundant cma_mutex lock"). The pageblock or (MAX_ORDER -1) from which we are trying to allocate memory may have already been acquired and isolated by others. Current cma_alloc() will then retry the next area by the step of bitmap_no + mask + 1 which are very likely within the same isolated range and fail again. So when the pageblock or MAX_ORDER is big (e.g. 8192), keep retrying in a small step become meaningless because it will be known to fail at a huge number of times due to the pageblock has been isolated by others, especially when allocating only one or two pages. Instread of looping in the same pageblock and wasting CPU mips a lot, especially for big pageblock system (e.g. 16M or 32M), we try the next MAX_ORDER_NR_PAGES directly. Doing this way can greatly mitigate the situtation. Below is the original error log during booting: [ 2.004804] cma: cma_alloc(cma (ptrval), count 1, align 0) [ 2.010318] cma: cma_alloc(cma (ptrval), count 1, align 0) [ 2.010776] cma: cma_alloc(): memory range at (ptrval) is busy, retrying [ 2.010785] cma: cma_alloc(): memory range at (ptrval) is busy, retrying [ 2.010793] cma: cma_alloc(): memory range at (ptrval) is busy, retrying [ 2.010800] cma: cma_alloc(): memory range at (ptrval) is busy, retrying [ 2.010807] cma: cma_alloc(): memory range at (ptrval) is busy, retrying [ 2.010814] cma: cma_alloc(): memory range at (ptrval) is busy, retrying .... (+1K retries) After fix, the 1200+ reties can be reduced to 0. Another test running 8 VPU decoder in parallel shows that 1500+ retries dropped to ~145. IOW this patch can improve the CMA allocation speed a lot when there're enough CMA memory by reducing retries significantly. Cc: Andrew Morton Cc: Marek Szyprowski Cc: Lecopzer Chen Cc: David Hildenbrand Cc: Vlastimil Babka CC: stable@vger.kernel.org # 5.11+ Fixes: a4efc174b382 ("mm/cma.c: remove redundant cma_mutex lock") Signed-off-by: Dong Aisheng --- v1->v2: * change to align with MAX_ORDER_NR_PAGES instead of pageblock_nr_pages --- mm/cma.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/cma.c b/mm/cma.c index 1c13a729d274..1251f65e2364 100644 --- a/mm/cma.c +++ b/mm/cma.c @@ -500,7 +500,9 @@ struct page *cma_alloc(struct cma *cma, unsigned long count, trace_cma_alloc_busy_retry(cma->name, pfn, pfn_to_page(pfn), count, align); /* try again with a bit different memory target */ - start = bitmap_no + mask + 1; + start = ALIGN(bitmap_no + mask + 1, + MAX_ORDER_NR_PAGES >> cma->order_per_bit); + } trace_cma_alloc_finish(cma->name, pfn, page, count, align);