On Fri, Jan 25, 2013 at 09:38:06AM +0800, Liu Bo wrote:
> On Thu, Jan 24, 2013 at 11:44:33AM -0500, Josef Bacik wrote:
> > On Tue, Jan 08, 2013 at 07:49:21AM -0700, Liu Bo wrote:
> > > During fsync, we put the changed parts(i.e. extent map) into the log tree,
> > > and we ship these parts from a list of modified_extents to a local list
> > > to process, of course, we must increment the refs of the extent maps to
> > > avoid it from getting evicted from cache.
> > >
> > > The problem is
> > > we don't hold the tree writer lock all the time of iterating the local
> > > list,
> > > and it is possible that other threads hack in and delete the extent map
> > > from
> > > the local list silently. So we'll end up with memory leak here.
> > >
> > > I hit this when testing xfstest 274 with mount options
> > > 'autodefrag,compress=zlib'.
> > >
> > > With this fix, the memory leak has gone away.
> >
> > This isn't going to work, we use the LOGGING flag to make sure the em isn't
> > merged as well. Thanks,
Well, never mind, I've seen the fix in your btrfs-next. But it'd be
better if you can also send it to the list where everyone can review it
easily.
thanks,
liubo
>
> A quick grep shows,
>
> 1 16 fs/btrfs/extent_map.h <<GLOBAL>>
> #define EXTENT_FLAG_LOGGING 4
> 2 406 fs/btrfs/extent_map.c <<remove_extent_mapping>>
> if (!test_bit(EXTENT_FLAG_LOGGING, &em->flags))
> 3 3403 fs/btrfs/tree-log.c <<btrfs_log_changed_extents>>
> set_bit(EXTENT_FLAG_LOGGING, &em->flags);
> 4 3413 fs/btrfs/tree-log.c <<btrfs_log_changed_extents>>
> clear_bit(EXTENT_FLAG_LOGGING, &em->flags);
>
> how does the flag avoid merging em?
>
> Seems we lost the check.
>
> static int mergable_maps(struct extent_map *prev, struct extent_map *next)
>
> {
>
> if (test_bit(EXTENT_FLAG_PINNED, &prev->flags))
>
> return 0;
>
>
>
> /*
>
> * don't merge compressed extents, we need to know their
>
> * actual size
>
> */
>
> if (test_bit(EXTENT_FLAG_COMPRESSED, &prev->flags))
>
> return 0;
>
>
> ...
> }
>
>
> thanks,
> liubo
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