mm: filemap: move lruvec accounting outside the xarray lock

__filemap_add_folio() inserts a folio and updates mapping->nrpages while
holding mapping->i_pages.xa_lock with interrupts disabled.  The XArray
insertion and nrpages update require the lock, but the lruvec statistic
updates do not.  With CONFIG_MEMCG, those calls also update per-CPU memcg
and lruvec counters and notify cgroup rstat, extending the critical
section.

Move the lruvec accounting after a successful XArray insertion and after
xas_unlock_irq().  The page-cache references pin the folio, while the
folio lock keeps folio->mapping stable and prevents removal until
accounting is complete.  This moves one lruvec update for ordinary folios
and a second for PMD-mappable folios out of the serialized section.

In a 30-second system-wide perf lock contention -ab capture on a
production host, the hottest caller-stack record attributed to
__filemap_add_folio() had 20,867 contentions and 557.930 ms total wait. 
That was 14% of the 3.998 seconds of aggregate lock wait in the capture. 
Moving lruvec accuting outside of critical section should help optimize
it.

Link: https://lore.kernel.org/20260916125122.2696271-1-usama.arif@linux.dev
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Muchun Song <muchun.song@linux.dev>
Reviewed-by: Vishal Moola (Fractile) <vishal.moola@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>

0 files changed, 0 insertions, 0 deletions