The patch titled
Subject: mm/page_alloc: treat RT tasks similar to __GFP_HIGH
has been added to the -mm mm-unstable branch. Its filename is
mm-page_alloc-treat-rt-tasks-similar-to-__gfp_high.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-treat-rt-tasks-similar-to-__gfp_high.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm/page_alloc: treat RT tasks similar to __GFP_HIGH
Date: Fri, 13 Jan 2023 11:12:13 +0000
RT tasks are allowed to dip below the min reserve but ALLOC_HARDER is
typically combined with ALLOC_MIN_RESERVE so RT tasks are a little
unusual. While there is some justification for allowing RT tasks access
to memory reserves, there is a strong chance that a RT task that is also
under memory pressure is at risk of missing deadlines anyway. Relax how
much reserves an RT task can access by treating it the same as __GFP_HIGH
allocations.
Note that in a future kernel release that the RT special casing will be
removed. Hard realtime tasks should be locking down resources in advance
and ensuring enough memory is available. Even a soft-realtime task like
audio or video live decoding which cannot jitter should be allocating both
memory and any disk space required up-front before the recording starts
instead of relying on reserves. At best, reserve access will only delay
the problem by a very short interval.
Link: https://lkml.kernel.org/r/20230113111217.14134-3-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: NeilBrown <neilb@xxxxxxx>
Cc: Thierry Reding <thierry.reding@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/mm/page_alloc.c~mm-page_alloc-treat-rt-tasks-similar-to-__gfp_high
+++ a/mm/page_alloc.c
@@ -4865,7 +4865,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
*/
alloc_flags &= ~ALLOC_CPUSET;
} else if (unlikely(rt_task(current)) && in_task())
- alloc_flags |= ALLOC_HARDER;
+ alloc_flags |= ALLOC_MIN_RESERVE;
alloc_flags = gfp_to_alloc_flags_cma(gfp_mask, alloc_flags);
_
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
