+ mm-page_alloc-explicitly-define-how-__gfp_high-non-blocking-allocations-accesses-reserves.patch added to mm-unstable branch

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



The patch titled
     Subject: mm/page_alloc: explicitly define how __GFP_HIGH non-blocking allocations accesses reserves
has been added to the -mm mm-unstable branch.  Its filename is
     mm-page_alloc-explicitly-define-how-__gfp_high-non-blocking-allocations-accesses-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-explicitly-define-how-__gfp_high-non-blocking-allocations-accesses-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@xxxxxxxxxxxxxxxxxxx>
Subject: mm/page_alloc: explicitly define how __GFP_HIGH non-blocking allocations accesses reserves
Date: Fri, 13 Jan 2023 11:12:16 +0000

GFP_ATOMIC allocations get flagged ALLOC_HARDER which is a vague
description.  In preparation for the removal of GFP_ATOMIC redefine
__GFP_ATOMIC to simply mean non-blocking and renaming ALLOC_HARDER to
ALLOC_NON_BLOCK accordingly.  __GFP_HIGH is required for access to
reserves but non-blocking is granted more access.  For example, GFP_NOWAIT
is non-blocking but has no special access to reserves.  A __GFP_NOFAIL
blocking allocation is granted access similar to __GFP_HIGH if the only
alternative is an OOM kill.

Link: https://lkml.kernel.org/r/20230113111217.14134-6-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: NeilBrown <neilb@xxxxxxx>
Cc: Thierry Reding <thierry.reding@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---


--- a/mm/internal.h~mm-page_alloc-explicitly-define-how-__gfp_high-non-blocking-allocations-accesses-reserves
+++ a/mm/internal.h
@@ -778,7 +778,10 @@ 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.
 				       */
@@ -793,7 +796,7 @@ 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-explicitly-define-how-__gfp_high-non-blocking-allocations-accesses-reserves
+++ a/mm/page_alloc.c
@@ -4007,18 +4007,19 @@ bool __zone_watermark_ok(struct zone *z,
 		 * __GFP_HIGH allows access to 50% of the min reserve as well
 		 * as OOM.
 		 */
-		if (alloc_flags & ALLOC_MIN_RESERVE)
+		if (alloc_flags & ALLOC_MIN_RESERVE) {
 			min -= min / 2;
 
-		/*
-		 * Non-blocking allocations can access some of the reserve
-		 * with more access if also __GFP_HIGH. The reasoning is that
-		 * a non-blocking caller may incur a more severe penalty
-		 * if it cannot get memory quickly, particularly if it's
-		 * also __GFP_HIGH.
-		 */
-		if (alloc_flags & ALLOC_HARDER)
-			min -= min / 4;
+			/*
+			 * Non-blocking allocations (e.g. GFP_ATOMIC) can
+			 * access more reserves than just __GFP_HIGH. Other
+			 * non-blocking allocations requests such as GFP_NOWAIT
+			 * or (GFP_KERNEL & ~__GFP_DIRECT_RECLAIM) do not get
+			 * access to the min reserve.
+			 */
+			if (alloc_flags & ALLOC_NON_BLOCK)
+				min -= min / 4;
+		}
 
 		/*
 		 * OOM victims can try even harder than the normal reserve
@@ -4869,28 +4870,30 @@ 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;
 
@@ -5321,12 +5324,13 @@ nopage:
 		WARN_ON_ONCE_GFP(costly_order, gfp_mask);
 
 		/*
-		 * Help non-failing allocations by giving them access to memory
-		 * reserves but do not use ALLOC_NO_WATERMARKS because this
+		 * Help non-failing allocations by giving some access to memory
+		 * 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_HARDER, ac);
+		page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_MIN_RESERVE, ac);
 		if (page)
 			goto got_pg;
 
_

Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx 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_alloc-explicitly-define-how-__gfp_high-non-blocking-allocations-accesses-reserves.patch




[Index of Archives]     [Kernel Archive]     [IETF Annouce]     [DCCP]     [Netdev]     [Networking]     [Security]     [Bugtraq]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux SCSI]

  Powered by Linux