Commit ffecfd1a (block: optionally snapshot page contents to provide
stable pages during write) uses bounce buffers for stable page writes in
jbd and ext3. Simplistically, __blk_queue_bounce takes a force parameter
that is used when pages must be snapshot.
Commit 6bc454d1 (bounce: Refactor __blk_queue_bounce to not use
bi_io_vec) refactored __blk_queue_bounce and now the start of the
function looks like this
static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
mempool_t *pool, int force)
{
struct bio *bio;
int rw = bio_data_dir(*bio_orig);
struct bio_vec *to, *from;
unsigned i;
bio_for_each_segment(from, *bio_orig, i)
if (page_to_pfn(from->bv_page) > queue_bounce_pfn(q))
goto bounce;
return;
bounce:
bio = bio_clone_bioset(*bio_orig, GFP_NOIO, fs_bio_set);
bio_for_each_segment_all(to, bio, i) {
struct page *page = to->bv_page;
if (page_to_pfn(page) <= queue_bounce_pfn(q) && !force)
continue;
Note that the first bio_for_each_segment is completely ignoring the
force parameter and hence snapshotting. This is particularly problematic
for ext3 which forces the use of MS_SNAP_STABLE.
I have not actually reproduced any problem, this is just code inspection
but it looks like commit 6bc454d1 broke ext3. Kent, why was the force
paramter ignored in that commit?
--
Mel Gorman
SUSE Labs
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