Neil's patch has been residing in mm-unstable as commit 2fafb4fe8f7a
("mm: discard __GFP_ATOMIC") for a long time and recently brought up
again. Most recently, I was worried that __GFP_HIGH allocations could
use high-order atomic reserves which is unintentional but there was no
response so lets revisit -- this series reworks how min reserves are used,
protects highorder reserves and then finishes with Neil's patch with very
minor modifications so it fits on top.
There was a review discussion on renaming __GFP_DIRECT_RECLAIM to
__GFP_ALLOW_BLOCKING but I didn't think it was that big an issue and is
ortogonal to the removal of __GFP_ATOMIC.
There were some concerns about how the gfp flags affect the min reserves
but it never reached a solid conclusion so I made my own attempt.
The series tries to iron out some of the details on how reserves are
used. ALLOC_HIGH becomes ALLOC_MIN_RESERVE and ALLOC_HARDER becomes
ALLOC_NON_BLOCK and documents how the reserves are affected. For example,
ALLOC_NON_BLOCK (no direct reclaim) on its own allows 25% of the min reserve.
ALLOC_MIN_RESERVE (__GFP_HIGH) allows 50% and both combined allows deeper
access again. ALLOC_OOM allows access to 75%.
High-order atomic allocations are explicitly handled with the caveat that
no __GFP_ATOMIC flag means that any high-order allocation that specifies
GFP_HIGH and cannot enter direct reclaim will be treated as if it was
GFP_ATOMIC.
--
2.35.3
From: NeilBrown <[email protected]>
__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/[email protected]
Signed-off-by: NeilBrown <[email protected]>
Signed-off-by: Mel Gorman <[email protected]>
---
Documentation/mm/balance.rst | 2 +-
drivers/iommu/tegra-smmu.c | 4 ++--
include/linux/gfp_types.h | 12 ++++--------
include/trace/events/mmflags.h | 1 -
lib/test_printf.c | 8 ++++----
mm/internal.h | 2 +-
mm/page_alloc.c | 13 +++----------
tools/perf/builtin-kmem.c | 1 -
8 files changed, 15 insertions(+), 28 deletions(-)
diff --git a/Documentation/mm/balance.rst b/Documentation/mm/balance.rst
index 6a1fadf3e173..e38e9d83c1c7 100644
--- a/Documentation/mm/balance.rst
+++ b/Documentation/mm/balance.rst
@@ -6,7 +6,7 @@ Memory Balancing
Started Jan 2000 by Kanoj Sarcar <[email protected]>
-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
diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
index 5b1af40221ec..af8d0e685260 100644
--- a/drivers/iommu/tegra-smmu.c
+++ b/drivers/iommu/tegra-smmu.c
@@ -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);
/*
diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h
index d88c46ca82e1..5088637fe5c2 100644
--- a/include/linux/gfp_types.h
+++ b/include/linux/gfp_types.h
@@ -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)
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index e87cb2b80ed3..11524cda4a95 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -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), \
diff --git a/lib/test_printf.c b/lib/test_printf.c
index 4bd15a593fbd..fe13de1bed5f 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -686,17 +686,17 @@ 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);
diff --git a/mm/internal.h b/mm/internal.h
index 98b1e526559d..48926b290cd5 100644
--- a/mm/internal.h
+++ b/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))
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6bee987ec9a3..ad6c4705a79d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4081,13 +4081,14 @@ 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,
@@ -5052,14 +5053,6 @@ __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;
diff --git a/tools/perf/builtin-kmem.c b/tools/perf/builtin-kmem.c
index ebfab2ca1702..4a06d83f2ac5 100644
--- a/tools/perf/builtin-kmem.c
+++ b/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" },
--
2.35.3
On 11/29/22 16:17, Mel Gorman wrote:
> From: NeilBrown <[email protected]>
>
> __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/[email protected]
> Signed-off-by: NeilBrown <[email protected]>
> Signed-off-by: Mel Gorman <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Just a nit below.
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4081,13 +4081,14 @@ 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
There's no GFP_HIGH. We could either keep GFP_ATOMIC here if we want to talk
about the high-level flag combo, or __GFP_HIGH if about the low-level
detail. We're deep in the page allocator implementation so the latter would
be OK.
> * 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
On Thu, Dec 08, 2022 at 07:17:48PM +0100, Vlastimil Babka wrote:
> > @@ -4081,13 +4081,14 @@ 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
>
> There's no GFP_HIGH. We could either keep GFP_ATOMIC here if we want to talk
> about the high-level flag combo, or __GFP_HIGH if about the low-level
> detail. We're deep in the page allocator implementation so the latter would
> be OK.
>
Fixed
--
Mel Gorman
SUSE Labs
Hi Mel,
On Tue, Nov 29, 2022 at 03:17:01PM +0000, Mel Gorman wrote:
> From: NeilBrown <[email protected]>
>
> __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/[email protected]
> Signed-off-by: NeilBrown <[email protected]>
> Signed-off-by: Mel Gorman <[email protected]>
> ---
> Documentation/mm/balance.rst | 2 +-
Documentation/core-api/memory-allocation.rst needs an update as well, and
there are other mentions of GFP_ATOMIC in Documentation/
> drivers/iommu/tegra-smmu.c | 4 ++--
> include/linux/gfp_types.h | 12 ++++--------
> include/trace/events/mmflags.h | 1 -
> lib/test_printf.c | 8 ++++----
> mm/internal.h | 2 +-
> mm/page_alloc.c | 13 +++----------
> tools/perf/builtin-kmem.c | 1 -
> 8 files changed, 15 insertions(+), 28 deletions(-)
>
> diff --git a/Documentation/mm/balance.rst b/Documentation/mm/balance.rst
> index 6a1fadf3e173..e38e9d83c1c7 100644
> --- a/Documentation/mm/balance.rst
> +++ b/Documentation/mm/balance.rst
> @@ -6,7 +6,7 @@ Memory Balancing
>
> Started Jan 2000 by Kanoj Sarcar <[email protected]>
>
> -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
> diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
> index 5b1af40221ec..af8d0e685260 100644
> --- a/drivers/iommu/tegra-smmu.c
> +++ b/drivers/iommu/tegra-smmu.c
> @@ -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);
>
> /*
> diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h
> index d88c46ca82e1..5088637fe5c2 100644
> --- a/include/linux/gfp_types.h
> +++ b/include/linux/gfp_types.h
> @@ -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)
> diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> index e87cb2b80ed3..11524cda4a95 100644
> --- a/include/trace/events/mmflags.h
> +++ b/include/trace/events/mmflags.h
> @@ -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), \
> diff --git a/lib/test_printf.c b/lib/test_printf.c
> index 4bd15a593fbd..fe13de1bed5f 100644
> --- a/lib/test_printf.c
> +++ b/lib/test_printf.c
> @@ -686,17 +686,17 @@ 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);
> diff --git a/mm/internal.h b/mm/internal.h
> index 98b1e526559d..48926b290cd5 100644
> --- a/mm/internal.h
> +++ b/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))
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6bee987ec9a3..ad6c4705a79d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4081,13 +4081,14 @@ 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,
> @@ -5052,14 +5053,6 @@ __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;
> diff --git a/tools/perf/builtin-kmem.c b/tools/perf/builtin-kmem.c
> index ebfab2ca1702..4a06d83f2ac5 100644
> --- a/tools/perf/builtin-kmem.c
> +++ b/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" },
> --
> 2.35.3
>
>
--
Sincerely yours,
Mike.
On Fri, 06 Jan 2023, Mike Rapoport wrote:
> Hi Mel,
>
> On Tue, Nov 29, 2022 at 03:17:01PM +0000, Mel Gorman wrote:
> > From: NeilBrown <[email protected]>
> >
> > __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/[email protected]
> > Signed-off-by: NeilBrown <[email protected]>
> > Signed-off-by: Mel Gorman <[email protected]>
> > ---
> > Documentation/mm/balance.rst | 2 +-
>
> Documentation/core-api/memory-allocation.rst needs an update as well, and
> there are other mentions of GFP_ATOMIC in Documentation/
Note that this patch removes __GFP_ATOMIC, but does not change the
behaviour of GFP_ATOMIC. So I don't believe there is any other
documentation that need changing.
Thanks,
NeilBrown
>
> > drivers/iommu/tegra-smmu.c | 4 ++--
> > include/linux/gfp_types.h | 12 ++++--------
> > include/trace/events/mmflags.h | 1 -
> > lib/test_printf.c | 8 ++++----
> > mm/internal.h | 2 +-
> > mm/page_alloc.c | 13 +++----------
> > tools/perf/builtin-kmem.c | 1 -
> > 8 files changed, 15 insertions(+), 28 deletions(-)
> >
> > diff --git a/Documentation/mm/balance.rst b/Documentation/mm/balance.rst
> > index 6a1fadf3e173..e38e9d83c1c7 100644
> > --- a/Documentation/mm/balance.rst
> > +++ b/Documentation/mm/balance.rst
> > @@ -6,7 +6,7 @@ Memory Balancing
> >
> > Started Jan 2000 by Kanoj Sarcar <[email protected]>
> >
> > -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
> > diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
> > index 5b1af40221ec..af8d0e685260 100644
> > --- a/drivers/iommu/tegra-smmu.c
> > +++ b/drivers/iommu/tegra-smmu.c
> > @@ -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);
> >
> > /*
> > diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h
> > index d88c46ca82e1..5088637fe5c2 100644
> > --- a/include/linux/gfp_types.h
> > +++ b/include/linux/gfp_types.h
> > @@ -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)
> > diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> > index e87cb2b80ed3..11524cda4a95 100644
> > --- a/include/trace/events/mmflags.h
> > +++ b/include/trace/events/mmflags.h
> > @@ -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), \
> > diff --git a/lib/test_printf.c b/lib/test_printf.c
> > index 4bd15a593fbd..fe13de1bed5f 100644
> > --- a/lib/test_printf.c
> > +++ b/lib/test_printf.c
> > @@ -686,17 +686,17 @@ 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);
> > diff --git a/mm/internal.h b/mm/internal.h
> > index 98b1e526559d..48926b290cd5 100644
> > --- a/mm/internal.h
> > +++ b/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))
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 6bee987ec9a3..ad6c4705a79d 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4081,13 +4081,14 @@ 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,
> > @@ -5052,14 +5053,6 @@ __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;
> > diff --git a/tools/perf/builtin-kmem.c b/tools/perf/builtin-kmem.c
> > index ebfab2ca1702..4a06d83f2ac5 100644
> > --- a/tools/perf/builtin-kmem.c
> > +++ b/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" },
> > --
> > 2.35.3
> >
> >
>
> --
> Sincerely yours,
> Mike.
>
On Thu, Jan 05, 2023 at 03:49:44PM +0200, Mike Rapoport wrote:
> Hi Mel,
>
> On Tue, Nov 29, 2022 at 03:17:01PM +0000, Mel Gorman wrote:
> > From: NeilBrown <[email protected]>
> >
> > __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/[email protected]
> > Signed-off-by: NeilBrown <[email protected]>
> > Signed-off-by: Mel Gorman <[email protected]>
> > ---
> > Documentation/mm/balance.rst | 2 +-
>
> Documentation/core-api/memory-allocation.rst needs an update as well, and
> there are other mentions of GFP_ATOMIC in Documentation/
>
What part do you think needs updating in that file?
There are two references to GFP_ATOMIC in that file, one about accessing
reserves and another about non-sleeping allocations and the accuracy
does not change after the series. If anything, this statement should
change because it invites GFP_ATOMIC abuse for spurious reasons
* If you think that accessing memory reserves is justified and the kernel
will be stressed unless allocation succeeds, you may use ``GFP_ATOMIC``.
There are other references to GFP_ATOMIC in Documentation/ that are are a
little inaccurate but not in a way that is harmful and is not changed by
the series. For example;
GFP_ATOMIC requests are kernel internal allocations that must
be satisfied, immediately. The kernel may drop some request,
in rare cases even panic, if a GFP_ATOMIC alloc fails.
This is a stronger statement than GFP_ATOMIC deserves but it's close enough
in the given context.
--
Mel Gorman
SUSE Labs
On Fri, Jan 06, 2023 at 09:35:24AM +0000, Mel Gorman wrote:
> On Thu, Jan 05, 2023 at 03:49:44PM +0200, Mike Rapoport wrote:
> > Hi Mel,
> >
> > On Tue, Nov 29, 2022 at 03:17:01PM +0000, Mel Gorman wrote:
> > > From: NeilBrown <[email protected]>
> > >
> > > __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/[email protected]
> > > Signed-off-by: NeilBrown <[email protected]>
> > > Signed-off-by: Mel Gorman <[email protected]>
> > > ---
> > > Documentation/mm/balance.rst | 2 +-
> >
> > Documentation/core-api/memory-allocation.rst needs an update as well, and
> > there are other mentions of GFP_ATOMIC in Documentation/
> >
>
> What part do you think needs updating in that file?
>
> There are two references to GFP_ATOMIC in that file, one about accessing
> reserves and another about non-sleeping allocations and the accuracy
> does not change after the series.
You are right, I got confused.
> If anything, this statement should change because it invites GFP_ATOMIC
> abuse for spurious reasons
>
> * If you think that accessing memory reserves is justified and the kernel
> will be stressed unless allocation succeeds, you may use ``GFP_ATOMIC``.
Care to send a patch? ;-)
> There are other references to GFP_ATOMIC in Documentation/ that are are a
> little inaccurate but not in a way that is harmful and is not changed by
> the series. For example;
>
> GFP_ATOMIC requests are kernel internal allocations that must
> be satisfied, immediately. The kernel may drop some request,
> in rare cases even panic, if a GFP_ATOMIC alloc fails.
>
> This is a stronger statement than GFP_ATOMIC deserves but it's close enough
> in the given context.
>
> --
> Mel Gorman
> SUSE Labs
>
--
Sincerely yours,
Mike.