On Wed, 2018-07-04 at 10:39 -0400, Mikulas Patocka wrote:
> This is backport of the upstream patch
> 41c73a49df31151f4ff868f28fe4f129f113fa2c. It should be backported to
> stable kernels because this performance problem was seen on the android
> 4.4 kernel.
Also queued this up for 3.16, thanks.
Ben.
> commit 41c73a49df31151f4ff868f28fe4f129f113fa2c
> Author: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Date: Wed Nov 23 17:04:00 2016 -0500
>
> dm bufio: drop the lock when doing GFP_NOIO allocation
>
> If the first allocation attempt using GFP_NOWAIT fails, drop the lock
> and retry using GFP_NOIO allocation (lock is dropped because the
> allocation can take some time).
>
> Note that we won't do GFP_NOIO allocation when we loop for the second
> time, because the lock shouldn't be dropped between __wait_for_free_buffer
> and __get_unclaimed_buffer.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
>
> diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
> index 9ef88f0e2382..1c2e1dd7ca16 100644
> --- a/drivers/md/dm-bufio.c
> +++ b/drivers/md/dm-bufio.c
> @@ -822,6 +822,7 @@ enum new_flag {
> static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client *c, enum new_flag nf)
> {
> struct dm_buffer *b;
> + bool tried_noio_alloc = false;
>
> /*
> * dm-bufio is resistant to allocation failures (it just keeps
> @@ -846,6 +847,15 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client
> if (nf == NF_PREFETCH)
> return NULL;
>
> + if (dm_bufio_cache_size_latch != 1 && !tried_noio_alloc) {
> + dm_bufio_unlock(c);
> + b = alloc_buffer(c, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
> + dm_bufio_lock(c);
> + if (b)
> + return b;
> + tried_noio_alloc = true;
> + }
> +
> if (!list_empty(&c->reserved_buffers)) {
> b = list_entry(c->reserved_buffers.next,
> struct dm_buffer, lru_list);
--
Ben Hutchings
Kids! Bringing about Armageddon can be dangerous. Do not attempt it
in your own home. - Terry Pratchett and Neil Gaiman, `Good Omens'
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