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H A Dmemory_hotplug.cdiff b92ca18e8ca596f4f3d80c1fe833bc57a1b2458c Mon Jun 28 21:42:12 CDT 2021 Mel Gorman <mgorman@techsingularity.net> mm/page_alloc: disassociate the pcp->high from pcp->batch

The pcp high watermark is based on the batch size but there is no
relationship between them other than it is convenient to use early in
boot.

This patch takes the first step and bases pcp->high on the zone low
watermark split across the number of CPUs local to a zone while the batch
size remains the same to avoid increasing allocation latencies. The
intent behind the default pcp->high is "set the number of PCP pages such
that if they are all full that background reclaim is not started
prematurely".

Note that in this patch the pcp->high values are adjusted after memory
hotplug events, min_free_kbytes adjustments and watermark scale factor
adjustments but not CPU hotplug events which is handled later in the
series.

On a test KVM instance;

Before grep -E "high:|batch" /proc/zoneinfo | tail -2
high: 378
batch: 63

After grep -E "high:|batch" /proc/zoneinfo | tail -2
high: 649
batch: 63

[mgorman@techsingularity.net: fix __setup_per_zone_wmarks for parallel memory
hotplug]
Link: https://lkml.kernel.org/r/20210528105925.GN30378@techsingularity.net

Link: https://lkml.kernel.org/r/20210525080119.5455-3-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
H A Dpage_alloc.cdiff b92ca18e8ca596f4f3d80c1fe833bc57a1b2458c Mon Jun 28 21:42:12 CDT 2021 Mel Gorman <mgorman@techsingularity.net> mm/page_alloc: disassociate the pcp->high from pcp->batch

The pcp high watermark is based on the batch size but there is no
relationship between them other than it is convenient to use early in
boot.

This patch takes the first step and bases pcp->high on the zone low
watermark split across the number of CPUs local to a zone while the batch
size remains the same to avoid increasing allocation latencies. The
intent behind the default pcp->high is "set the number of PCP pages such
that if they are all full that background reclaim is not started
prematurely".

Note that in this patch the pcp->high values are adjusted after memory
hotplug events, min_free_kbytes adjustments and watermark scale factor
adjustments but not CPU hotplug events which is handled later in the
series.

On a test KVM instance;

Before grep -E "high:|batch" /proc/zoneinfo | tail -2
high: 378
batch: 63

After grep -E "high:|batch" /proc/zoneinfo | tail -2
high: 649
batch: 63

[mgorman@techsingularity.net: fix __setup_per_zone_wmarks for parallel memory
hotplug]
Link: https://lkml.kernel.org/r/20210528105925.GN30378@techsingularity.net

Link: https://lkml.kernel.org/r/20210525080119.5455-3-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>