Commit 2973d822 authored by NeilBrown's avatar NeilBrown Committed by Andrew Morton
Browse files

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
 - 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: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 1ebbb218

Documentation/mm/balance.rst

+1 −1
Original line number Diff line number Diff line
@@ -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

drivers/iommu/tegra-smmu.c

+2 −2
Original line number Diff line number Diff line
@@ -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);



	/*

include/linux/gfp_types.h

+4 −8
Original line number Diff line number Diff line
@@ -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)

include/trace/events/mmflags.h

+0 −1
Original line number Diff line number Diff line
@@ -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),		\

lib/test_printf.c

+4 −4
Original line number Diff line number Diff line
@@ -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);