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6.5: mm patches #2

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merged 8 commits into from
Sep 23, 2023
Merged

6.5: mm patches #2

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406ce3e
mm: Disable watermark boosting by default
kerneltoast Mar 28, 2020
5d27c2a
mm: Stop kswapd early when nothing's waiting for it to free pages
kerneltoast Apr 20, 2020
e7ce283
mm: Don't stop kswapd on a per-node basis when there are no waiters
kerneltoast May 20, 2020
5dbfdf0
mm: Increment kswapd_waiters for throttled direct reclaimers
kerneltoast Jul 17, 2021
2e3cb1a
mm: Disable proactive compaction by default
kerneltoast Oct 25, 2020
8253fa2
mm: Don't hog the CPU and zone lock in rmqueue_bulk()
kerneltoast Oct 21, 2021
e22ced7
scatterlist: Don't allocate sg lists using __get_free_page
kerneltoast Sep 5, 2020
132f9fd
mm: Omit RCU read lock in list_lru_count_one() when RCU isn't needed
kerneltoast Sep 26, 2021
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mm: Disable watermark boosting by default 
What watermark boosting does is preemptively fire up kswapd to free
memory when there hasn't been an allocation failure. It does this by
increasing kswapd's high watermark goal and then firing up kswapd. The
reason why this causes freezes is because, with the increased high
watermark goal, kswapd will steal memory from processes that need it in
order to make forward progress. These processes will, in turn, try to
allocate memory again, which will cause kswapd to steal necessary pages
from those processes again, in a positive feedback loop known as page
thrashing. When page thrashing occurs, your system is essentially
livelocked until the necessary forward progress can be made to stop
processes from trying to continuously allocate memory and trigger
kswapd to steal it back.

This problem already occurs with kswapd *without* watermark boosting,
but it's usually only encountered on machines with a small amount of
memory and/or a slow CPU. Watermark boosting just makes the existing
problem worse enough to notice on higher spec'd machines.

Disable watermark boosting by default since it's a total dumpster fire.
I can't imagine why anyone would want to explicitly enable it, but the
option is there in case someone does.

Signed-off-by: Sultan Alsawaf <[email protected]>
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@kerneltoast @Rasenkai
kerneltoast authored and Rasenkai committed Sep 23, 2023
commit 406ce3efae53acb226b5a085a442097cc381d947
2 changes: 1 addition & 1 deletion mm/page_alloc.c
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Expand Up @@ -297,7 +297,7 @@ static compound_page_dtor * const compound_page_dtors[NR_COMPOUND_DTORS] = {

int min_free_kbytes = 1024;
int user_min_free_kbytes = -1;
static int watermark_boost_factor __read_mostly = 15000;
static int watermark_boost_factor __read_mostly;
static int watermark_scale_factor = 10;

/* movable_zone is the "real" zone pages in ZONE_MOVABLE are taken from */
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