| Message ID | 164692725757.2097000.2060513769492301854.stgit@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | afs: Fix potential thrashing in afs writeback | expand |
On Thu, Mar 10, 2022 at 11:47 AM David Howells <dhowells@redhat.com> wrote: > > In afs_writepages_region(), if the dirty page we find is undergoing > writeback or write to cache, but the sync_mode is WB_SYNC_NONE, we go round > the loop trying the same page again and again with no pausing or waiting > unless and until another thread manages to clear the writeback and fscache > flags. > > Fix this with three measures: > > (1) Advance the start to after the page we found. > > (2) Break out of the loop and return if rescheduling is requested. > > (3) Arbitrarily give up after a maximum of 5 skips. > > Fixes: 31143d5d515e ("AFS: implement basic file write support") > Reported-by: Marc Dionne <marc.dionne@auristor.com> > Signed-off-by: David Howells <dhowells@redhat.com> > --- > > fs/afs/write.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/fs/afs/write.c b/fs/afs/write.c > index 85c9056ba9fb..bd0201f4939a 100644 > --- a/fs/afs/write.c > +++ b/fs/afs/write.c > @@ -701,7 +701,7 @@ static int afs_writepages_region(struct address_space *mapping, > struct folio *folio; > struct page *head_page; > ssize_t ret; > - int n; > + int n, skips = 0; > > _enter("%llx,%llx,", start, end); > > @@ -752,8 +752,15 @@ static int afs_writepages_region(struct address_space *mapping, > #ifdef CONFIG_AFS_FSCACHE > folio_wait_fscache(folio); > #endif > + } else { > + start += folio_size(folio); > } > folio_put(folio); > + if (wbc->sync_mode == WB_SYNC_NONE) { > + if (skips >= 5 || need_resched()) > + break; > + skips++; > + } > continue; > } Looks good in testing, the problem would show up in xfstests generic/285. Tested-by: Marc Dionne <marc.dionne@auristor.com> Acked-by: Marc Dionne <marc.dionne@auristor.com> Marc
diff --git a/fs/afs/write.c b/fs/afs/write.c index 85c9056ba9fb..bd0201f4939a 100644 --- a/fs/afs/write.c +++ b/fs/afs/write.c @@ -701,7 +701,7 @@ static int afs_writepages_region(struct address_space *mapping, struct folio *folio; struct page *head_page; ssize_t ret; - int n; + int n, skips = 0; _enter("%llx,%llx,", start, end); @@ -752,8 +752,15 @@ static int afs_writepages_region(struct address_space *mapping, #ifdef CONFIG_AFS_FSCACHE folio_wait_fscache(folio); #endif + } else { + start += folio_size(folio); } folio_put(folio); + if (wbc->sync_mode == WB_SYNC_NONE) { + if (skips >= 5 || need_resched()) + break; + skips++; + } continue; }
In afs_writepages_region(), if the dirty page we find is undergoing writeback or write to cache, but the sync_mode is WB_SYNC_NONE, we go round the loop trying the same page again and again with no pausing or waiting unless and until another thread manages to clear the writeback and fscache flags. Fix this with three measures: (1) Advance the start to after the page we found. (2) Break out of the loop and return if rescheduling is requested. (3) Arbitrarily give up after a maximum of 5 skips. Fixes: 31143d5d515e ("AFS: implement basic file write support") Reported-by: Marc Dionne <marc.dionne@auristor.com> Signed-off-by: David Howells <dhowells@redhat.com> --- fs/afs/write.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)