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Commit 933f01d4 authored by Milan Broz's avatar Milan Broz Committed by Alasdair G Kergon
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dm crypt: avoid unnecessary wait when splitting bio 



Don't wait between submitting crypt requests for a bio unless
we are short of memory.

There are two situations when we must split an encrypted bio:
  1) there are no free pages;
  2) the new bio would violate underlying device restrictions
(e.g. max hw segments).

In case (2) we do not need to wait.

Add output variable to crypt_alloc_buffer() to distinguish between
these cases.

Signed-off-by: default avatarMilan Broz <mbroz@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent c8081618

drivers/md/dm-crypt.c

+18 −8
Original line number Diff line number Diff line
@@ -457,9 +457,11 @@ static void dm_crypt_bio_destructor(struct bio *bio) 
/*

 * Generate a new unfragmented bio with the given size

 * This should never violate the device limitations

 * May return a smaller bio when running out of pages

 * May return a smaller bio when running out of pages, indicated by

 * *out_of_pages set to 1.

 */

static struct bio *crypt_alloc_buffer(struct dm_crypt_io *io, unsigned size)

static struct bio *crypt_alloc_buffer(struct dm_crypt_io *io, unsigned size,

				      unsigned *out_of_pages)

{

	struct crypt_config *cc = io->target->private;

	struct bio *clone;
@@ -473,11 +475,14 @@ static struct bio *crypt_alloc_buffer(struct dm_crypt_io *io, unsigned size) 
		return NULL;



	clone_init(io, clone);

	*out_of_pages = 0;



	for (i = 0; i < nr_iovecs; i++) {

		page = mempool_alloc(cc->page_pool, gfp_mask);

		if (!page)

		if (!page) {

			*out_of_pages = 1;

			break;

		}



		/*

		 * if additional pages cannot be allocated without waiting,
@@ -696,6 +701,7 @@ static void kcryptd_crypt_write_convert(struct dm_crypt_io *io) 
	struct crypt_config *cc = io->target->private;

	struct bio *clone;

	int crypt_finished;

	unsigned out_of_pages = 0;

	unsigned remaining = io->base_bio->bi_size;

	int r;
@@ -710,7 +716,7 @@ static void kcryptd_crypt_write_convert(struct dm_crypt_io *io) 
	 * so repeat the whole process until all the data can be handled.

	 */

	while (remaining) {

		clone = crypt_alloc_buffer(io, remaining);

		clone = crypt_alloc_buffer(io, remaining, &out_of_pages);

		if (unlikely(!clone)) {

			io->error = -ENOMEM;

			break;
@@ -737,11 +743,15 @@ static void kcryptd_crypt_write_convert(struct dm_crypt_io *io) 
				break;

		}



		/* out of memory -> run queues */

		if (unlikely(remaining)) {

			wait_event(cc->writeq, !atomic_read(&io->ctx.pending));

		/*

		 * Out of memory -> run queues

		 * But don't wait if split was due to the io size restriction

		 */

		if (unlikely(out_of_pages))

			congestion_wait(WRITE, HZ/100);

		}



		if (unlikely(remaining))

			wait_event(cc->writeq, !atomic_read(&io->ctx.pending));

	}



	crypt_dec_pending(io);