Re: [PATCH] ext4: isolate s_orphan_lock from read-mostly fields

From: Jonas Zhou <redacted>

s_orphan_lock is modified by orphan-list operations, but currently shares
a cache line with s_journal and s_ext4_flags.  The latter fields are read
from common ext4 paths, so unrelated accesses can cause the line containing
the lock to bounce between CPUs.

On a two-socket Intel Xeon Silver 4208 system with 16 workers, throughput
improved by 4.6% for stress-ng.dnotify and 1.7% for stress-ng.unlink.  Perf
c2c showed that HITM events on the affected fields decreased from 3,699 to
3,125 (-15.5%) for stress-ng.dnotify and from 1,368 to 571 (-58.3%) for
stress-ng.unlink.  Remote HITM events decreased by 45.1% and 65.5%,
respectively.  The journal/flags line had no remote HITM events after the
change; the remaining remote HITM events were on the orphan-lock line.

Signed-off-by: Jonas Zhou <redacted>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260903021836.962624-1-jonaszhou-oc@zhaoxin.com?part=1