When a file system becomes fragmented (using MythTV, for example), the
bigalloc window searching ends up causing huge performance problems. In
a file system presented by a user experiencing this bug, the file system
was 90% free, but no 32-block free windows existed on the entire file system.
This causes the allocator to scan the entire file system for each 128k write
before backing down to searching for individual blocks.
In the end, finding a contiguous window for all the blocks in a write is
an advantageous special case, but one that can be found naturally when
such a window exists anyway.
This patch removes the bigalloc window searching, and has been proven to fix
the test case described above.
Signed-off-by: Jeff Mahoney <[email protected]>
diff -ruNp linux-2.6.18-rc4.orig/fs/reiserfs/bitmap.c linux-2.6.18-rc4.orig.devel/fs/reiserfs/bitmap.c
--- linux-2.6.18-rc4.orig/fs/reiserfs/bitmap.c 2006-08-22 09:49:45.000000000 -0400
+++ linux-2.6.18-rc4.orig.devel/fs/reiserfs/bitmap.c 2006-08-22 10:19:35.000000000 -0400
@@ -1019,7 +1019,6 @@ static inline int blocknrs_and_prealloc_
b_blocknr_t finish = SB_BLOCK_COUNT(s) - 1;
int passno = 0;
int nr_allocated = 0;
- int bigalloc = 0;
determine_prealloc_size(hint);
if (!hint->formatted_node) {
@@ -1046,28 +1045,9 @@ static inline int blocknrs_and_prealloc_
hint->preallocate = hint->prealloc_size = 0;
}
/* for unformatted nodes, force large allocations */
- bigalloc = amount_needed;
}
do {
- /* in bigalloc mode, nr_allocated should stay zero until
- * the entire allocation is filled
- */
- if (unlikely(bigalloc && nr_allocated)) {
- reiserfs_warning(s, "bigalloc is %d, nr_allocated %d\n",
- bigalloc, nr_allocated);
- /* reset things to a sane value */
- bigalloc = amount_needed - nr_allocated;
- }
- /*
- * try pass 0 and pass 1 looking for a nice big
- * contiguous allocation. Then reset and look
- * for anything you can find.
- */
- if (passno == 2 && bigalloc) {
- passno = 0;
- bigalloc = 0;
- }
switch (passno++) {
case 0: /* Search from hint->search_start to end of disk */
start = hint->search_start;
@@ -1105,8 +1085,7 @@ static inline int blocknrs_and_prealloc_
new_blocknrs +
nr_allocated,
start, finish,
- bigalloc ?
- bigalloc : 1,
+ 1,
amount_needed -
nr_allocated,
hint->
--
Jeff Mahoney
SUSE Labs
-
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