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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: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Milan Broz 2008-10-10 13:37:08 +01:00 committed by Alasdair G Kergon
parent c8081618a9
commit 933f01d433
1 changed files with 18 additions and 8 deletions
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26
drivers/md/dm-crypt.c
View File

@ -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);