Messages in this thread Patch in this message | | | Date | Tue, 22 Aug 2006 10:28:20 -0400 | From | Jeff Mahoney <> | Subject | [PATCH] reiserfs: eliminate minimum window size for bitmap searching |
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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 <jeffm@suse.com>
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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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