[Devel] [PATCH] dm-qcow2: use kvmalloc for bvec allocation during rq splitting

[Alexey Kuznetsov]

Hello!

Does not it make sense to go there only when order is !0. Or even > 1.

Also, what's about dm-ploop? It has the same problem, is not it?

On Wed, Jun 25, 2025 at 8:41 PM Andrey Zhadchenko
<andrey.zhadchenko at virtuozzo.com> wrote:
>
> as we saw up to 32768 bios in a single request. kmalloc with
> GFP_NOIO simply fails on a loaded system.
>
> [ 1351.057243] kworker/u9:8: page allocation failure: order:6, mode:0x40c00(GFP_NOIO|__GFP_COMP), nodemask=(null),cpuset=/,mems_allowed=0
> [ 1351.058056] CPU: 2 PID: 12720 Comm: kworker/u9:8 ve: / Kdump: loaded Tainted: G               X  -------  ---  5.14.0-427.44.1.vz9.80.39 #1 80.39
> [ 1351.058543] Hardware name: Acronis OpenStack Compute/Virtuozzo, BIOS 1.16.1-1.vz9.2 04/01/2014
> [ 1351.058936] Workqueue: dm-qcow2 do_qcow2_work [dm_qcow2]
> [ 1351.059214] Call Trace:
> [ 1351.059390]  <TASK>
> [ 1351.059560]  dump_stack_lvl+0x34/0x48
> [ 1351.059762]  warn_alloc+0x138/0x160
> [ 1351.059982]  ? __alloc_pages_direct_compact+0xa7/0x280
> [ 1351.060259]  __alloc_pages_slowpath.constprop.0+0x76f/0x7e0
> [ 1351.060543]  __alloc_pages+0x3bb/0x3f0
> [ 1351.060759]  ? create_bvec_from_rq+0x8f/0x130 [dm_qcow2]
> [ 1351.061011]  __kmalloc_large_node+0x79/0x100
> [ 1351.061231]  __kmalloc+0xca/0x140
> [ 1351.061430]  create_bvec_from_rq+0x8f/0x130 [dm_qcow2]
> [ 1351.061679]  do_qcow2_work+0x3cd/0xbc0 [dm_qcow2]
> [ 1351.061925]  ? trigger_cpulimit_balance+0x6b/0x180
> [ 1351.062167]  ? _raw_spin_unlock+0xa/0x30
> [ 1351.062391]  ? finish_task_switch.isra.0+0x8c/0x2a0
> [ 1351.062625]  process_one_work+0x1e5/0x3b0
> [ 1351.062838]  worker_thread+0x50/0x3a0
> [ 1351.063044]  ? __pfx_worker_thread+0x10/0x10
> [ 1351.063321]  kthread+0xe0/0x100
> [ 1351.063516]  ? __pfx_kthread+0x10/0x10
> [ 1351.063713]  ret_from_fork+0x2c/0x50
> [ 1351.063935]  </TASK>
>
> Also update ploop to use kvmalloc for the same purpose.
>
> https://virtuozzo.atlassian.net/browse/VSTOR-109363
> Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
> ---
>  drivers/md/dm-ploop-map.c | 6 +++---
>  drivers/md/dm-qcow2-map.c | 6 +++---
>  2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
> index 35085a04ca5f..89f8d527150d 100644
> --- a/drivers/md/dm-ploop-map.c
> +++ b/drivers/md/dm-ploop-map.c
> @@ -194,7 +194,7 @@ static void ploop_prq_endio(struct pio *pio, void *prq_ptr,
>         struct request *rq = prq->rq;
>
>         if (prq->bvec)
> -               kfree(prq->bvec);
> +               kvfree(prq->bvec);
>         if (prq->css)
>                 css_put(prq->css);
>         /*
> @@ -1963,8 +1963,8 @@ static struct bio_vec *ploop_create_bvec_from_rq(struct request *rq)
>         rq_for_each_bvec(bv, rq, rq_iter)
>                 nr_bvec++;
>
> -       bvec = kmalloc_array(nr_bvec, sizeof(struct bio_vec),
> -                            GFP_ATOMIC);
> +       bvec = kvmalloc_array(nr_bvec, sizeof(struct bio_vec),
> +                             GFP_ATOMIC);
>         if (!bvec)
>                 goto out;
>
> diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
> index f7cb036bb416..80552e2ab734 100644
> --- a/drivers/md/dm-qcow2-map.c
> +++ b/drivers/md/dm-qcow2-map.c
> @@ -3501,8 +3501,8 @@ static struct bio_vec *create_bvec_from_rq(struct request *rq)
>         rq_for_each_bvec(bv, rq, rq_iter)
>                 nr_bvec++;
>
> -       bvec = kmalloc_array(nr_bvec, sizeof(struct bio_vec),
> -                            GFP_NOIO);
> +       bvec = kvmalloc_array(nr_bvec, sizeof(struct bio_vec),
> +                             GFP_NOIO);
>         if (!bvec)
>                 goto out;
>
> @@ -4188,7 +4188,7 @@ static void qrq_endio(struct qcow2_target *tgt, struct qio *qio,
>         struct request *rq = qrq->rq;
>
>         if (qrq->bvec)
> -               kfree(qrq->bvec);
> +               kvfree(qrq->bvec);
>         /*
>          * Here is exit point for rq, and here we handle ENOSPC.
>          * Embedded qios will be reinitialized like they've just
> --
> 2.43.0
>
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