+ mm-page_alloc-give-gfp_atomic-and-non-blocking-allocations-access-to-reserves.patch added to mm-unstable branch

+ mm-page_alloc-give-gfp_atomic-and-non-blocking-allocations-access-to-reserves.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/page_alloc: give GFP_ATOMIC and non-blocking allocations access to reserves
has been added to the -mm mm-unstable branch.  Its filename is
     mm-page_alloc-give-gfp_atomic-and-non-blocking-allocations-access-to-reserves.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_alloc-give-gfp_atomic-and-non-blocking-allocations-access-to-reserves.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Mel Gorman <mgorman@techsingularity.net>
Subject: mm/page_alloc: give GFP_ATOMIC and non-blocking allocations access to reserves
Date: Mon, 9 Jan 2023 15:16:30 +0000

Explicit GFP_ATOMIC allocations get flagged ALLOC_HARDER which is a bit
vague.  In preparation for removing __GFP_ATOMIC, give GFP_ATOMIC and
other non-blocking allocation requests equal access to reserve.  Rename
ALLOC_HARDER to ALLOC_NON_BLOCK to make it more clear what the flag means.

Link: https://lkml.kernel.org/r/20230109151631.24923-7-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: NeilBrown <neilb@suse.de>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/internal.h   |    7 +++++--
 mm/page_alloc.c |   23 +++++++++++++----------
 2 files changed, 18 insertions(+), 12 deletions(-)

--- a/mm/internal.h~mm-page_alloc-give-gfp_atomic-and-non-blocking-allocations-access-to-reserves
+++ a/mm/internal.h
@@ -760,7 +760,10 @@ unsigned int reclaim_clean_pages_from_li
 #define ALLOC_OOM		ALLOC_NO_WATERMARKS
 #endif
 
-#define ALLOC_HARDER		 0x10 /* try to alloc harder */
+#define ALLOC_NON_BLOCK		 0x10 /* Caller cannot block. Allow access
+				       * to 25% of the min watermark or
+				       * 62.5% if __GFP_HIGH is set.
+				       */
 #define ALLOC_MIN_RESERVE	 0x20 /* __GFP_HIGH set. Allow access to 50%
 				       * of the min watermark.
 				       */
@@ -775,7 +778,7 @@ unsigned int reclaim_clean_pages_from_li
 #define ALLOC_KSWAPD		0x800 /* allow waking of kswapd, __GFP_KSWAPD_RECLAIM set */
 
 /* Flags that allow allocations below the min watermark. */
-#define ALLOC_RESERVES (ALLOC_HARDER|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM)
+#define ALLOC_RESERVES (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM)
 
 enum ttu_flags;
 struct tlbflush_unmap_batch;
--- a/mm/page_alloc.c~mm-page_alloc-give-gfp_atomic-and-non-blocking-allocations-access-to-reserves
+++ a/mm/page_alloc.c
@@ -4014,7 +4014,7 @@ bool __zone_watermark_ok(struct zone *z,
 		 * if it cannot get memory quickly, particularly if it's
 		 * also __GFP_HIGH.
 		 */
-		if (alloc_flags & ALLOC_HARDER)
+		if (alloc_flags & ALLOC_NON_BLOCK)
 			min -= min / 4;
 
 		/*
@@ -4866,28 +4866,30 @@ gfp_to_alloc_flags(gfp_t gfp_mask, unsig
 	 * 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_MIN_RESERVE(__GFP_HIGH).
+	 * set both ALLOC_NON_BLOCK and ALLOC_MIN_RESERVE(__GFP_HIGH).
 	 */
 	alloc_flags |= (__force int)
 		(gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM));
 
-	if (gfp_mask & __GFP_ATOMIC) {
+	if (!(gfp_mask & __GFP_DIRECT_RECLAIM)) {
 		/*
 		 * Not worth trying to allocate harder for __GFP_NOMEMALLOC even
 		 * if it can't schedule.
 		 */
 		if (!(gfp_mask & __GFP_NOMEMALLOC)) {
-			alloc_flags |= ALLOC_HARDER;
+			alloc_flags |= ALLOC_NON_BLOCK;
 
 			if (order > 0)
 				alloc_flags |= ALLOC_HIGHATOMIC;
 		}
 
 		/*
-		 * Ignore cpuset mems for GFP_ATOMIC rather than fail, see the
-		 * comment for __cpuset_node_allowed().
+		 * Ignore cpuset mems for non-blocking __GFP_HIGH (probably
+		 * GFP_ATOMIC) rather than fail, see the comment for
+		 * __cpuset_node_allowed().
 		 */
-		alloc_flags &= ~ALLOC_CPUSET;
+		if (alloc_flags & ALLOC_MIN_RESERVE)
+			alloc_flags &= ~ALLOC_CPUSET;
 	} else if (unlikely(rt_task(current)) && in_task())
 		alloc_flags |= ALLOC_MIN_RESERVE;
 
@@ -5319,11 +5321,12 @@ nopage:
 
 		/*
 		 * Help non-failing allocations by giving them access to memory
-		 * reserves but do not use ALLOC_NO_WATERMARKS because this
+		 * reserves normally used for high priority non-blocking
+		 * allocations but do not use ALLOC_NO_WATERMARKS because this
 		 * could deplete whole memory reserves which would just make
-		 * the situation worse
+		 * the situation worse.
 		 */
-		page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_MIN_RESERVE|ALLOC_HARDER, ac);
+		page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_MIN_RESERVE|ALLOC_NON_BLOCK, ac);
 		if (page)
 			goto got_pg;
 
_

Patches currently in -mm which might be from mgorman@techsingularity.net are

mm-page_alloc-rename-alloc_high-to-alloc_min_reserve.patch
mm-page_alloc-treat-rt-tasks-similar-to-__gfp_high.patch
mm-page_alloc-explicitly-record-high-order-atomic-allocations-in-alloc_flags.patch
mm-page_alloc-explicitly-define-what-alloc-flags-deplete-min-reserves.patch
mm-page_allocc-allow-__gfp_nofail-requests-deeper-access-to-reserves.patch
mm-page_alloc-give-gfp_atomic-and-non-blocking-allocations-access-to-reserves.patch