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md: deal with merge_bvec_fn in component devices better.

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If a component device has a merge_bvec_fn then as we never call it
we must ensure we never need to.  Currently this is done by setting
max_sector to 1 PAGE, however this does not stop a bio being created
with several sub-page iovecs that would violate the merge_bvec_fn.

So instead set max_segments to 1 and set the segment boundary to the
same as a page boundary to ensure there is only ever one single-page
segment of IO requested at a time.

This can particularly be an issue when 'xen' is used as it is
known to submit multiple small buffers in a single bio.

Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@kernel.org
This commit is contained in:
NeilBrown
2010-03-08 16:44:38 +11:00
parent 25cf84cf37
commit 627a2d3c29
5 changed files with 60 additions and 41 deletions
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12
drivers/md/linear.c
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@@ -172,12 +172,14 @@ static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
disk_stack_limits(mddev->gendisk, rdev->bdev,
rdev->data_offset << 9);
/* as we don't honour merge_bvec_fn, we must never risk
* violating it, so limit ->max_sector to one PAGE, as
* a one page request is never in violation.
* violating it, so limit max_segments to 1 lying within
* a single page.
*/
if (rdev->bdev->bd_disk->queue->merge_bvec_fn &&
queue_max_sectors(mddev->queue) > (PAGE_SIZE>>9))
blk_queue_max_hw_sectors(mddev->queue, PAGE_SIZE>>9);
if (rdev->bdev->bd_disk->queue->merge_bvec_fn) {
blk_queue_max_segments(mddev->queue, 1);
blk_queue_segment_boundary(mddev->queue,
PAGE_CACHE_SIZE - 1);
}
conf->array_sectors += rdev->sectors;
cnt++;