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Message-Id: <20220430113028.9daeebeedf679aa384da5945@linux-foundation.org>
Date: Sat, 30 Apr 2022 11:30:28 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Michal Hocko <mhocko@...e.com>
Cc: NeilBrown <neilb@...e.de>,
Thierry Reding <thierry.reding@...il.com>,
Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] MM: discard __GFP_ATOMIC
Folks,
Discussion seemed to meander then peter out. What's the thinking on
this patch now?
Thanks.
From: "NeilBrown" <neilb@...e.de>
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 <neilb@...e.de>
Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Thierry Reding <thierry.reding@...il.com>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
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 <kanoj@....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
--- 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
@@ -3918,12 +3918,12 @@ 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,
@@ -4657,12 +4657,12 @@ 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.
@@ -4855,14 +4855,6 @@ __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" },
_
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