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netfs: Record contention stats for writeback lock

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Record statistics for contention upon the writeback serialisation lock that
prevents racing writeback calls from causing each other to interleave their
writebacks.  These can be viewed in /proc/fs/netfs/stats on the WbLock line,
with skip=N indicating the number of non-SYNC writebacks skipped and wait=N
indicating the number of SYNC writebacks that waited.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Steve French <sfrench@samba.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/20240814203850.2240469-5-dhowells@redhat.com/ # v2
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
David Howells 2024-05-31 15:48:29 +01:00 committed by Christian Brauner
parent 43ebbf9393
commit ef966d73fb
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
3 changed files with 14 additions and 3 deletions
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2
fs/netfs/internal.h
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@ -117,6 +117,8 @@ extern atomic_t netfs_n_wh_upload_failed;
extern atomic_t netfs_n_wh_write;
extern atomic_t netfs_n_wh_write_done;
extern atomic_t netfs_n_wh_write_failed;
extern atomic_t netfs_n_wb_lock_skip;
extern atomic_t netfs_n_wb_lock_wait;
int netfs_stats_show(struct seq_file *m, void *v);

5
fs/netfs/stats.c
View File

@ -39,6 +39,8 @@ atomic_t netfs_n_wh_upload_failed;
atomic_t netfs_n_wh_write;
atomic_t netfs_n_wh_write_done;
atomic_t netfs_n_wh_write_failed;
atomic_t netfs_n_wb_lock_skip;
atomic_t netfs_n_wb_lock_wait;
int netfs_stats_show(struct seq_file *m, void *v)
{
@ -78,6 +80,9 @@ int netfs_stats_show(struct seq_file *m, void *v)
atomic_read(&netfs_n_rh_rreq),
atomic_read(&netfs_n_rh_sreq),
atomic_read(&netfs_n_wh_wstream_conflict));
seq_printf(m, "WbLock : skip=%u wait=%u\n",
atomic_read(&netfs_n_wb_lock_skip),
atomic_read(&netfs_n_wb_lock_wait));
return fscache_stats_show(m);
}
EXPORT_SYMBOL(netfs_stats_show);

10
fs/netfs/write_issue.c
View File

@ -505,10 +505,14 @@ int netfs_writepages(struct address_space *mapping,
struct folio *folio;
int error = 0;
if (wbc->sync_mode == WB_SYNC_ALL)
if (!mutex_trylock(&ictx->wb_lock)) {
if (wbc->sync_mode == WB_SYNC_NONE) {
netfs_stat(&netfs_n_wb_lock_skip);
return 0;
}
netfs_stat(&netfs_n_wb_lock_wait);
mutex_lock(&ictx->wb_lock);
else if (!mutex_trylock(&ictx->wb_lock))
return 0;
}
/* Need the first folio to be able to set up the op. */
folio = writeback_iter(mapping, wbc, NULL, &error);