On 10.06.23 00:35, Andrew Morton wrote:
On Wed, 31 May 2023 10:51:01 +0800 "zhaoyang.huang" <zhaoyang.huang@xxxxxxxxxx> wrote:
From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
This patch fixes unproductive reclaiming of CMA pages by skipping them when they
are not available for current context. It is arise from bellowing OOM issue, which
caused by large proportion of MIGRATE_CMA pages among free pages.
[ 36.172486] [03-19 10:05:52.172] ActivityManager: page allocation failure: order:0, mode:0xc00(GFP_NOIO), nodemask=(null),cpuset=foreground,mems_allowed=0
[ 36.189447] [03-19 10:05:52.189] DMA32: 0*4kB 447*8kB (C) 217*16kB (C) 124*32kB (C) 136*64kB (C) 70*128kB (C) 22*256kB (C) 3*512kB (C) 0*1024kB 0*2048kB 0*4096kB = 35848kB
[ 36.193125] [03-19 10:05:52.193] Normal: 231*4kB (UMEH) 49*8kB (MEH) 14*16kB (H) 13*32kB (H) 8*64kB (H) 2*128kB (H) 0*256kB 1*512kB (H) 0*1024kB 0*2048kB 0*4096kB = 3236kB
...
[ 36.234447] [03-19 10:05:52.234] SLUB: Unable to allocate memory on node -1, gfp=0xa20(GFP_ATOMIC)
[ 36.234455] [03-19 10:05:52.234] cache: ext4_io_end, object size: 64, buffer size: 64, default order: 0, min order: 0
[ 36.234459] [03-19 10:05:52.234] node 0: slabs: 53,objs: 3392, free: 0
We saw plenty of feedback for earlier versions, but now silence. Does
this mean we're all OK with v5?
The logic kind-of makes sense to me (but the kswapd special-casing
already shows that it might be a bit fragile for future use), but I did
not yet figure out if this actually fixes something or is a pure
performance improvement.
As we phrased it in the comment "It is waste of effort", but in the
patch description "This patch fixes unproductive reclaiming" + a scary
dmesg.
Am I correct that this is a pure performance optimization (and the issue
revealed itself in that OOM report), or does this actually *fix* something?
If it's a performance improvement, it would be good to show that it is
an actual improvement worth the churn ...
--
Cheers,
David / dhildenb
