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Commit 9ea0f949 authored by Jeff Mahoney's avatar Jeff Mahoney Committed by Linus Torvalds
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[PATCH] reiserfs: eliminate minimum window size for bitmap searching 



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: default avatarJeff Mahoney <jeffm@suse.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 5a2618e6

fs/reiserfs/bitmap.c

+1 −22
Original line number Original line Diff line number Diff line
@@ -1034,7 +1034,6 @@ static inline int blocknrs_and_prealloc_arrays_from_search_start 
	b_blocknr_t finish = SB_BLOCK_COUNT(s) - 1;

	b_blocknr_t finish = SB_BLOCK_COUNT(s) - 1;

	int passno = 0;

	int passno = 0;

	int nr_allocated = 0;

	int nr_allocated = 0;

	int bigalloc = 0;





	determine_prealloc_size(hint);

	determine_prealloc_size(hint);

	if (!hint->formatted_node) {

	if (!hint->formatted_node) {
@@ -1061,28 +1060,9 @@ static inline int blocknrs_and_prealloc_arrays_from_search_start 
				hint->preallocate = hint->prealloc_size = 0;

				hint->preallocate = hint->prealloc_size = 0;

		}

		}

		/* for unformatted nodes, force large allocations */

		/* for unformatted nodes, force large allocations */

		bigalloc = amount_needed;

	}

	}





	do {

	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++) {

		switch (passno++) {

		case 0:	/* Search from hint->search_start to end of disk */

		case 0:	/* Search from hint->search_start to end of disk */

			start = hint->search_start;

			start = hint->search_start;
@@ -1120,8 +1100,7 @@ static inline int blocknrs_and_prealloc_arrays_from_search_start 
								 new_blocknrs +

								 new_blocknrs +

								 nr_allocated,

								 nr_allocated,

								 start, finish,

								 start, finish,

								 bigalloc ?

								 1,

								 bigalloc : 1,

								 amount_needed -

								 amount_needed -

								 nr_allocated,

								 nr_allocated,

								 hint->

								 hint->