From: "NeilBrown" Subject: mm: discard __GFP_ATOMIC __GFP_ATOMIC serves little purpose. Its main effect is to set ALLOC_HARDER which adds a few little boosts to increase the chance of an allocation succeeding, one of which is to lower the water-mark at which it will succeed. It is *always* paired with __GFP_HIGH which sets ALLOC_HIGH which also adjusts this watermark. It is probable that other users of __GFP_HIGH should benefit from the other little bonuses that __GFP_ATOMIC gets. __GFP_ATOMIC also gives a warning if used with __GFP_DIRECT_RECLAIM. There is little point to this. We already get a might_sleep() warning if __GFP_DIRECT_RECLAIM is set. __GFP_ATOMIC allows the "watermark_boost" to be side-stepped. It is probable that testing ALLOC_HARDER is a better fit here. __GFP_ATOMIC is used by tegra-smmu.c to check if the allocation might sleep. This should test __GFP_DIRECT_RECLAIM instead. This patch: - removes __GFP_ATOMIC - causes __GFP_HIGH to set ALLOC_HARDER unless __GFP_NOMEMALLOC is set (as well as ALLOC_HIGH). - makes other adjustments as suggested by the above. The net result is not change to GFP_ATOMIC allocations. Other allocations that use __GFP_HIGH will benefit from a few different extra privileges. This affects: xen, dm, md, ntfs3 the vermillion frame buffer hibernation ksm swap all of which likely produce more benefit than cost if these selected allocation are more likely to succeed quickly. Link: https://lkml.kernel.org/r/163712397076.13692.4727608274002939094@noble.neil.brown.name Signed-off-by: NeilBrown Reviewed-by: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Thierry Reding Cc: Mel Gorman Signed-off-by: Andrew Morton --- Documentation/vm/balance.rst | 2 +- drivers/iommu/tegra-smmu.c | 4 ++-- include/linux/gfp.h | 12 ++++-------- include/trace/events/mmflags.h | 1 - lib/test_printf.c | 8 ++++---- mm/internal.h | 2 +- mm/page_alloc.c | 16 ++++------------ tools/include/linux/gfp.h | 3 +-- tools/perf/builtin-kmem.c | 1 - 9 files changed, 17 insertions(+), 32 deletions(-) --- a/Documentation/vm/balance.rst~mm-discard-__gfp_atomic +++ a/Documentation/vm/balance.rst @@ -6,7 +6,7 @@ Memory Balancing Started Jan 2000 by Kanoj Sarcar -Memory balancing is needed for !__GFP_ATOMIC and !__GFP_KSWAPD_RECLAIM as +Memory balancing is needed for !__GFP_HIGH and !__GFP_KSWAPD_RECLAIM as well as for non __GFP_IO allocations. The first reason why a caller may avoid reclaim is that the caller can not --- a/drivers/iommu/tegra-smmu.c~mm-discard-__gfp_atomic +++ a/drivers/iommu/tegra-smmu.c @@ -671,12 +671,12 @@ static struct page *as_get_pde_page(stru * allocate page in a sleeping context if GFP flags permit. Hence * spinlock needs to be unlocked and re-locked after allocation. */ - if (!(gfp & __GFP_ATOMIC)) + if (gfp & __GFP_DIRECT_RECLAIM) spin_unlock_irqrestore(&as->lock, *flags); page = alloc_page(gfp | __GFP_DMA | __GFP_ZERO); - if (!(gfp & __GFP_ATOMIC)) + if (gfp & __GFP_DIRECT_RECLAIM) spin_lock_irqsave(&as->lock, *flags); /* --- a/include/linux/gfp.h~mm-discard-__gfp_atomic +++ a/include/linux/gfp.h @@ -39,7 +39,7 @@ struct vm_area_struct; #define ___GFP_IO 0x40u #define ___GFP_FS 0x80u #define ___GFP_ZERO 0x100u -#define ___GFP_ATOMIC 0x200u +/* 0x200u unused */ #define ___GFP_DIRECT_RECLAIM 0x400u #define ___GFP_KSWAPD_RECLAIM 0x800u #define ___GFP_WRITE 0x1000u @@ -124,11 +124,8 @@ struct vm_area_struct; * * %__GFP_HIGH indicates that the caller is high-priority and that granting * the request is necessary before the system can make forward progress. - * For example, creating an IO context to clean pages. - * - * %__GFP_ATOMIC indicates that the caller cannot reclaim or sleep and is - * high priority. Users are typically interrupt handlers. This may be - * used in conjunction with %__GFP_HIGH + * For example creating an IO context to clean pages and requests + * from atomic context. * * %__GFP_MEMALLOC allows access to all memory. This should only be used when * the caller guarantees the allocation will allow more memory to be freed @@ -143,7 +140,6 @@ struct vm_area_struct; * %__GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves. * This takes precedence over the %__GFP_MEMALLOC flag if both are set. */ -#define __GFP_ATOMIC ((__force gfp_t)___GFP_ATOMIC) #define __GFP_HIGH ((__force gfp_t)___GFP_HIGH) #define __GFP_MEMALLOC ((__force gfp_t)___GFP_MEMALLOC) #define __GFP_NOMEMALLOC ((__force gfp_t)___GFP_NOMEMALLOC) @@ -337,7 +333,7 @@ struct vm_area_struct; * version does not attempt reclaim/compaction at all and is by default used * in page fault path, while the non-light is used by khugepaged. */ -#define GFP_ATOMIC (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM) +#define GFP_ATOMIC (__GFP_HIGH|__GFP_KSWAPD_RECLAIM) #define GFP_KERNEL (__GFP_RECLAIM | __GFP_IO | __GFP_FS) #define GFP_KERNEL_ACCOUNT (GFP_KERNEL | __GFP_ACCOUNT) #define GFP_NOWAIT (__GFP_KSWAPD_RECLAIM) --- a/include/trace/events/mmflags.h~mm-discard-__gfp_atomic +++ a/include/trace/events/mmflags.h @@ -29,7 +29,6 @@ {(unsigned long)__GFP_HIGHMEM, "__GFP_HIGHMEM"}, \ {(unsigned long)GFP_DMA32, "GFP_DMA32"}, \ {(unsigned long)__GFP_HIGH, "__GFP_HIGH"}, \ - {(unsigned long)__GFP_ATOMIC, "__GFP_ATOMIC"}, \ {(unsigned long)__GFP_IO, "__GFP_IO"}, \ {(unsigned long)__GFP_FS, "__GFP_FS"}, \ {(unsigned long)__GFP_NOWARN, "__GFP_NOWARN"}, \ --- a/lib/test_printf.c~mm-discard-__gfp_atomic +++ a/lib/test_printf.c @@ -673,17 +673,17 @@ flags(void) gfp = GFP_ATOMIC|__GFP_DMA; test("GFP_ATOMIC|GFP_DMA", "%pGg", &gfp); - gfp = __GFP_ATOMIC; - test("__GFP_ATOMIC", "%pGg", &gfp); + gfp = __GFP_HIGH; + test("__GFP_HIGH", "%pGg", &gfp); /* Any flags not translated by the table should remain numeric */ gfp = ~__GFP_BITS_MASK; snprintf(cmp_buffer, BUF_SIZE, "%#lx", (unsigned long) gfp); test(cmp_buffer, "%pGg", &gfp); - snprintf(cmp_buffer, BUF_SIZE, "__GFP_ATOMIC|%#lx", + snprintf(cmp_buffer, BUF_SIZE, "__GFP_HIGH|%#lx", (unsigned long) gfp); - gfp |= __GFP_ATOMIC; + gfp |= __GFP_HIGH; test(cmp_buffer, "%pGg", &gfp); kfree(cmp_buffer); --- a/mm/internal.h~mm-discard-__gfp_atomic +++ a/mm/internal.h @@ -24,7 +24,7 @@ struct folio_batch; #define GFP_RECLAIM_MASK (__GFP_RECLAIM|__GFP_HIGH|__GFP_IO|__GFP_FS|\ __GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_NOFAIL|\ __GFP_NORETRY|__GFP_MEMALLOC|__GFP_NOMEMALLOC|\ - __GFP_ATOMIC|__GFP_NOLOCKDEP) + __GFP_NOLOCKDEP) /* The GFP flags allowed during early boot */ #define GFP_BOOT_MASK (__GFP_BITS_MASK & ~(__GFP_RECLAIM|__GFP_IO|__GFP_FS)) --- a/mm/page_alloc.c~mm-discard-__gfp_atomic +++ a/mm/page_alloc.c @@ -3966,12 +3966,12 @@ static inline bool zone_watermark_fast(s free_pages)) return true; /* - * Ignore watermark boosting for GFP_ATOMIC order-0 allocations + * Ignore watermark boosting for GFP_HIGH order-0 allocations * when checking the min watermark. The min watermark is the * point where boosting is ignored so that kswapd is woken up * when below the low watermark. */ - if (unlikely(!order && (gfp_mask & __GFP_ATOMIC) && z->watermark_boost + if (unlikely(!order && (alloc_flags & ALLOC_HARDER) && z->watermark_boost && ((alloc_flags & ALLOC_WMARK_MASK) == WMARK_MIN))) { mark = z->_watermark[WMARK_MIN]; return __zone_watermark_ok(z, order, mark, highest_zoneidx, @@ -4702,12 +4702,12 @@ gfp_to_alloc_flags(gfp_t gfp_mask) * The caller may dip into page reserves a bit more if the caller * cannot run direct reclaim, or if the caller has realtime scheduling * policy or is asking for __GFP_HIGH memory. GFP_ATOMIC requests will - * set both ALLOC_HARDER (__GFP_ATOMIC) and ALLOC_HIGH (__GFP_HIGH). + * set both ALLOC_HARDER (unless __GFP_NOMEMALLOC) and ALLOC_HIGH. */ alloc_flags |= (__force int) (gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM)); - if (gfp_mask & __GFP_ATOMIC) { + if (gfp_mask & __GFP_HIGH) { /* * Not worth trying to allocate harder for __GFP_NOMEMALLOC even * if it can't schedule. @@ -4900,14 +4900,6 @@ __alloc_pages_slowpath(gfp_t gfp_mask, u unsigned int cpuset_mems_cookie; int reserve_flags; - /* - * We also sanity check to catch abuse of atomic reserves being used by - * callers that are not in atomic context. - */ - if (WARN_ON_ONCE((gfp_mask & (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)) == - (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM))) - gfp_mask &= ~__GFP_ATOMIC; - retry_cpuset: compaction_retries = 0; no_progress_loops = 0; --- a/tools/include/linux/gfp.h~mm-discard-__gfp_atomic +++ a/tools/include/linux/gfp.h @@ -12,7 +12,6 @@ #define __GFP_FS 0x80u #define __GFP_NOWARN 0x200u #define __GFP_ZERO 0x8000u -#define __GFP_ATOMIC 0x80000u #define __GFP_ACCOUNT 0x100000u #define __GFP_DIRECT_RECLAIM 0x400000u #define __GFP_KSWAPD_RECLAIM 0x2000000u @@ -20,7 +19,7 @@ #define __GFP_RECLAIM (__GFP_DIRECT_RECLAIM | __GFP_KSWAPD_RECLAIM) #define GFP_ZONEMASK 0x0fu -#define GFP_ATOMIC (__GFP_HIGH | __GFP_ATOMIC | __GFP_KSWAPD_RECLAIM) +#define GFP_ATOMIC (__GFP_HIGH | __GFP_KSWAPD_RECLAIM) #define GFP_KERNEL (__GFP_RECLAIM | __GFP_IO | __GFP_FS) #define GFP_NOWAIT (__GFP_KSWAPD_RECLAIM) --- a/tools/perf/builtin-kmem.c~mm-discard-__gfp_atomic +++ a/tools/perf/builtin-kmem.c @@ -640,7 +640,6 @@ static const struct { { "__GFP_HIGHMEM", "HM" }, { "GFP_DMA32", "D32" }, { "__GFP_HIGH", "H" }, - { "__GFP_ATOMIC", "_A" }, { "__GFP_IO", "I" }, { "__GFP_FS", "F" }, { "__GFP_NOWARN", "NWR" }, _