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mm: discard __GFP_ATOMIC

Browse source 
__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
 - allows __GFP_HIGH allocations to ignore watermark boosting as well
   as GFP_ATOMIC requests.
 - 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.

[mgorman: Minor adjustments to rework on top of a series]
Link: https://lkml.kernel.org/r/163712397076.13692.4727608274002939094@noble.neil.brown.name
Link: https://lkml.kernel.org/r/20230113111217.14134-7-mgorman@techsingularity.net
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
NeilBrown 2023-01-13 11:12:17 +00:00 • committed by Andrew Morton
parent 1ebbb21811
commit 2973d8229b
8 changed files with 15 additions and 28 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
Documentation/mm/balance.rst
View file

@ -6,7 +6,7 @@ Memory Balancing
Started Jan 2000 by Kanoj Sarcar <kanoj@sgi.com>
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

4
drivers/iommu/tegra-smmu.c
View file

@ -671,12 +671,12 @@ static struct page *as_get_pde_page(struct tegra_smmu_as *as,
* 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 (gfpflags_allow_blocking(gfp))
spin_unlock_irqrestore(&as->lock, *flags);
page = alloc_page(gfp | __GFP_DMA | __GFP_ZERO);
if (!(gfp & __GFP_ATOMIC))
if (gfpflags_allow_blocking(gfp))
spin_lock_irqsave(&as->lock, *flags);
/*

12
include/linux/gfp_types.h
View file

@ -31,7 +31,7 @@ typedef unsigned int __bitwise gfp_t;
#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
@ -116,11 +116,8 @@ typedef unsigned int __bitwise gfp_t;
*
* %__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
@ -135,7 +132,6 @@ typedef unsigned int __bitwise gfp_t;
* %__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)
@ -329,7 +325,7 @@ typedef unsigned int __bitwise gfp_t;
* 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)

1
include/trace/events/mmflags.h
View file

@ -31,7 +31,6 @@
gfpflag_string(__GFP_HIGHMEM), \
gfpflag_string(GFP_DMA32), \
gfpflag_string(__GFP_HIGH), \
gfpflag_string(__GFP_ATOMIC), \
gfpflag_string(__GFP_IO), \
gfpflag_string(__GFP_FS), \
gfpflag_string(__GFP_NOWARN), \

8
lib/test_printf.c
View file

@ -674,17 +674,17 @@ 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);

2
mm/internal.h
View file

@ -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))

13
mm/page_alloc.c
View file

@ -4105,13 +4105,14 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
if (__zone_watermark_ok(z, order, mark, highest_zoneidx, alloc_flags,
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_MIN_RESERVE) && z->watermark_boost
&& ((alloc_flags & ALLOC_WMARK_MASK) == WMARK_MIN))) {
mark = z->_watermark[WMARK_MIN];
return __zone_watermark_ok(z, order, mark, highest_zoneidx,
@ -5076,14 +5077,6 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
unsigned int zonelist_iter_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;
restart:
compaction_retries = 0;
no_progress_loops = 0;

1
tools/perf/builtin-kmem.c
View file

@ -653,7 +653,6 @@ static const struct {
{ "__GFP_HIGHMEM", "HM" },
{ "GFP_DMA32", "D32" },
{ "__GFP_HIGH", "H" },
{ "__GFP_ATOMIC", "_A" },
{ "__GFP_IO", "I" },
{ "__GFP_FS", "F" },
{ "__GFP_NOWARN", "NWR" },