linux-kernel - [PATCH] Should GFP_ATOMIC fail when we're below low watermark?

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Message-Id: <200708201138.50508.nigel@nigel.suspend2.net>
Date:	Mon, 20 Aug 2007 11:38:49 +1000
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] Should GFP_ATOMIC fail when we're below low watermark?

Hi all.

In current git (and for a while now), an attempt to allocate memory with 
GFP_ATOMIC will fail if we're below the low watermark level. The only way to 
access that memory that I can see (not that I've looked that hard) is to have 
PF_MEMALLOC set (ie from kswapd). I'm wondering if this behaviour is correct. 
Shouldn't GFP_ATOMIC allocations ignore watermarks too? How about GFP_KERNEL?

The following patch is a potential fix for GFP_ATOMIC.

Regards,

Nigel

Signed-off-by: Nigel Cunningham <nigel@...el.suspend2.net>

 page_alloc.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
diff -ruNp 995-gfp-atomic-alloc.patch-old/mm/page_alloc.c 995-gfp-atomic-alloc.patch-new/mm/page_alloc.c
--- 995-gfp-atomic-alloc.patch-old/mm/page_alloc.c	2007-08-20 11:14:34.000000000 +1000
+++ 995-gfp-atomic-alloc.patch-new/mm/page_alloc.c	2007-08-20 11:11:09.000000000 +1000
@@ -1286,8 +1286,8 @@ restart:
 	/* This allocation should allow future memory freeing. */

 rebalance:
-	if (((p->flags & PF_MEMALLOC) || unlikely(test_thread_flag(TIF_MEMDIE)))
-			&& !in_interrupt()) {
+	if (((p->flags & PF_MEMALLOC) || unlikely(test_thread_flag(TIF_MEMDIE)) ||
+			(gfp_mask & GFP_ATOMIC)) && !in_interrupt()) {
 		if (!(gfp_mask & __GFP_NOMEMALLOC)) {
 nofail_alloc:
 			/* go through the zonelist yet again, ignoring mins */

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