On 28-Nov-24 10:01 AM, Mateusz Guzik wrote:
WIlly mentioned the folio wait queue hash table could be grown, you
can find it in mm/filemap.c:
1062 #define PAGE_WAIT_TABLE_BITS 8
1063 #define PAGE_WAIT_TABLE_SIZE (1 << PAGE_WAIT_TABLE_BITS)
1064 static wait_queue_head_t folio_wait_table[PAGE_WAIT_TABLE_SIZE]
__cacheline_aligned;
1065
1066 static wait_queue_head_t *folio_waitqueue(struct folio *folio)
1067 {
1068 │ return &folio_wait_table[hash_ptr(folio, PAGE_WAIT_TABLE_BITS)];
1069 }
Can you collect off cpu time? offcputime-bpfcc -K > /tmp/out
Flamegraph for "perf record --off-cpu -F 99 -a -g --all-kernel --kernel-callchains -- sleep 120" is attached.
Off-cpu samples were collected for 120s at around 45th minute run of the FIO benchmark that actually runs for 1hr. This run was with kernel that had your inode_lock fix but no changes to PAGE_WAIT_TABLE_BITS.
Hopefully this captures the representative sample of the scalability issue with folio lock.
Regards, Bharata.
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