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 <>
Signed-off-by: default avatarAlasdair G Kergon <>
parent c8081618
......@@ -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;
* 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;
......@@ -737,11 +743,15 @@ static void kcryptd_crypt_write_convert(struct dm_crypt_io *io)
/* 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));
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