xfs: limit maxlen based on available space in xfs_rtallocate_extent_near()

xfs_rtallocate_extent_near() calls xfs_rtallocate_extent_block() with
the minlen and maxlen that were passed to it.
xfs_rtallocate_extent_block() then scans the bitmap block looking for a
free range of size maxlen. If there is none, it has to scan the whole
bitmap block before returning the largest range of at least size minlen.
For a fragmented realtime device and a large allocation request, it's
almost certain that this will have to search the whole bitmap block,
leading to high CPU usage.

However, the realtime summary tells us the maximum size available in the
bitmap block. We can limit the search in xfs_rtallocate_extent_block()
to that size and often stop before scanning the whole bitmap block.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index c774a4ccdd150806da22069e54def0b4688e8f2b..3aa9634a9e76cb9fe7161d8aac41e3330ea29cf2 100644 (file)
--- a/fs/xfs/xfs_rtalloc.c
+++ b/fs/xfs/xfs_rtalloc.c
@@ -497,6 +497,9 @@ xfs_rtallocate_extent_near(
                 * allocating one.
                 */
                if (maxlog >= 0) {
+                       xfs_extlen_t maxavail =
+                               min_t(xfs_rtblock_t, maxlen,
+                                     (1ULL << (maxlog + 1)) - 1);
                        /*
                         * On the positive side of the starting location.
                         */
@@ -506,7 +509,7 @@ xfs_rtallocate_extent_near(
                                 * this block.
                                 */
                                error = xfs_rtallocate_extent_block(args,
-                                               bbno + i, minlen, maxlen, len,
+                                               bbno + i, minlen, maxavail, len,
                                                &n, prod, &r);
                                if (error) {
                                        return error;
@@ -553,7 +556,7 @@ xfs_rtallocate_extent_near(
                                                continue;
                                        error = xfs_rtallocate_extent_block(args,
                                                        bbno + j, minlen,
-                                                       maxlen, len, &n, prod,
+                                                       maxavail, len, &n, prod,
                                                        &r);
                                        if (error) {
                                                return error;
@@ -575,7 +578,7 @@ xfs_rtallocate_extent_near(
                                 * that we found.
                                 */
                                error = xfs_rtallocate_extent_block(args,
-                                               bbno + i, minlen, maxlen, len,
+                                               bbno + i, minlen, maxavail, len,
                                                &n, prod, &r);
                                if (error) {
                                        return error;