From: Chi Zhiling chizhiling@kylinos.cn
commit 3ef22684038aa577c10972ee9c6a2455f5fac941 upstream.
Recently, we found that the CPU spent a lot of time in xfs_alloc_ag_vextent_size when the filesystem has millions of fragmented spaces.
The reason is that we conducted much extra searching for extents that could not yield a better result, and these searches would cost a lot of time when there were millions of extents to search through. Even if we get the same result length, we don't switch our choice to the new one, so we can definitely terminate the search early.
Since the result length cannot exceed the found length, when the found length equals the best result length we already have, we can conclude the search.
We did a test in that filesystem: [root@localhost ~]# xfs_db -c freesp /dev/vdb from to extents blocks pct 1 1 215 215 0.01 2 3 994476 1988952 99.99
Before this patch: 0) | xfs_alloc_ag_vextent_size [xfs]() { 0) * 15597.94 us | }
After this patch: 0) | xfs_alloc_ag_vextent_size [xfs]() { 0) 19.176 us | }
Signed-off-by: Chi Zhiling chizhiling@kylinos.cn Reviewed-by: Dave Chinner dchinner@redhat.com Signed-off-by: Carlos Maiolino cem@kernel.org Signed-off-by: Catherine Hoang catherine.hoang@oracle.com Acked-by: Darrick J. Wong djwong@kernel.org --- fs/xfs/libxfs/xfs_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c index d8081095557c..ad2fa3c26f8a 100644 --- a/fs/xfs/libxfs/xfs_alloc.c +++ b/fs/xfs/libxfs/xfs_alloc.c @@ -1783,7 +1783,7 @@ xfs_alloc_ag_vextent_size( error = -EFSCORRUPTED; goto error0; } - if (flen < bestrlen) + if (flen <= bestrlen) break; busy = xfs_alloc_compute_aligned(args, fbno, flen, &rbno, &rlen, &busy_gen);