Re: [PATCH 2/6] MM: improve documentation for __GFP_NOFAIL
From: Vlastimil Babka <hidden>
Date: 2021-10-05 09:20:56
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linux-ext4, linux-fsdevel, linux-mm, linux-nfs, linux-xfs, lkml
On 9/17/21 04:56, NeilBrown wrote:
__GFP_NOFAIL is documented both in gfp.h and memory-allocation.rst. The details are not entirely consistent. This patch ensures both places state that: - there is a risk of deadlock with reclaim/writeback/oom-kill - it should only be used when there is no real alternative - it is preferable to an endless loop - it is strongly discourages for costly-order allocations. Signed-off-by: NeilBrown <redacted>
Acked-by: Vlastimil Babka <redacted> Nit below:
quoted hunk ↗ jump to hunk
diff --git a/include/linux/gfp.h b/include/linux/gfp.h index 55b2ec1f965a..1d2a89e20b8b 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h@@ -209,7 +209,11 @@ struct vm_area_struct; * used only when there is no reasonable failure policy) but it is * definitely preferable to use the flag rather than opencode endless * loop around allocator. - * Using this flag for costly allocations is _highly_ discouraged. + * Use of this flag may lead to deadlocks if locks are held which would + * be needed for memory reclaim, write-back, or the timely exit of a + * process killed by the OOM-killer. Dropping any locks not absolutely + * needed is advisable before requesting a %__GFP_NOFAIL allocate. + * Using this flag for costly allocations (order>1) is _highly_ discouraged.
We define costly as 3, not 1. But sure it's best to avoid even order>0 for __GFP_NOFAIL. Advising order>1 seems arbitrary though?
*/ #define __GFP_IO ((__force gfp_t)___GFP_IO) #define __GFP_FS ((__force gfp_t)___GFP_FS)