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authorOmar Sandoval <osandov@fb.com>2023-10-16 20:47:04 +0300
committerDarrick J. Wong <djwong@kernel.org>2023-10-19 18:34:33 +0300
commit85fa2c774397b98f5dc65a4ed6ab17c1a15db158 (patch)
tree5aab3c63b54251147f7b9e0275d4a5b59919a367 /fs/xfs
parentec5857bf07639a03d32b8ecb346df634925f8bc2 (diff)
downloadlinux-85fa2c774397b98f5dc65a4ed6ab17c1a15db158.tar.xz
xfs: don't try redundant allocations in xfs_rtallocate_extent_near()
xfs_rtallocate_extent_near() tries to find a free extent as close to a target bitmap block given by bbno as possible, which may be before or after bbno. Searching backwards has a complication: the realtime summary accounts for free space _starting_ in a bitmap block, but not straddling or ending in a bitmap block. So, when the negative search finds a free extent in the realtime summary, in order to end up closer to the target, it looks for the end of the free extent. For example, if bbno - 2 has a free extent, then it will check bbno - 1, then bbno - 2. But then if bbno - 3 has a free extent, it will check bbno - 1 again, then bbno - 2 again, and then bbno - 3. This results in a quadratic loop, which is completely pointless since the repeated checks won't find anything new. Fix it by remembering where we last checked up to and continue from there. This also obviates the need for a check of the realtime summary. 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>
Diffstat (limited to 'fs/xfs')
-rw-r--r--fs/xfs/xfs_rtalloc.c54
1 files changed, 7 insertions, 47 deletions
diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
index 3aa9634a9e76..b743da885ed6 100644
--- a/fs/xfs/xfs_rtalloc.c
+++ b/fs/xfs/xfs_rtalloc.c
@@ -477,6 +477,7 @@ xfs_rtallocate_extent_near(
}
bbno = xfs_rtx_to_rbmblock(mp, start);
i = 0;
+ j = -1;
ASSERT(minlen != 0);
log2len = xfs_highbit32(minlen);
/*
@@ -527,33 +528,13 @@ xfs_rtallocate_extent_near(
*/
else { /* i < 0 */
/*
- * Loop backwards through the bitmap blocks from
- * the starting point-1 up to where we are now.
- * There should be an extent which ends in this
- * bitmap block and is long enough.
+ * Loop backwards through the bitmap blocks
+ * from where we last checked down to where we
+ * are now. There should be an extent which
+ * ends in this bitmap block and is long
+ * enough.
*/
- for (j = -1; j > i; j--) {
- /*
- * Grab the summary information for
- * this bitmap block.
- */
- error = xfs_rtany_summary(args,
- log2len,
- mp->m_rsumlevels - 1,
- bbno + j, &maxlog);
- if (error) {
- return error;
- }
- /*
- * If there's no extent given in the
- * summary that means the extent we
- * found must carry over from an
- * earlier block. If there is an
- * extent given, we've already tried
- * that allocation, don't do it again.
- */
- if (maxlog >= 0)
- continue;
+ for (; j >= i; j--) {
error = xfs_rtallocate_extent_block(args,
bbno + j, minlen,
maxavail, len, &n, prod,
@@ -569,27 +550,6 @@ xfs_rtallocate_extent_near(
return 0;
}
}
- /*
- * There weren't intervening bitmap blocks
- * with a long enough extent, or the
- * allocation didn't work for some reason
- * (i.e. it's a little * too short).
- * Try to allocate from the summary block
- * that we found.
- */
- error = xfs_rtallocate_extent_block(args,
- bbno + i, minlen, maxavail, len,
- &n, prod, &r);
- if (error) {
- return error;
- }
- /*
- * If it works, return the extent.
- */
- if (r != NULLRTEXTNO) {
- *rtx = r;
- return 0;
- }
}
}
/*