Hi Coly,
Thanks for the patch!
> On Apr 2, 2020, at 1:13 AM, Coly Li <colyli@xxxxxxx> wrote:
>
> Commit b330e6a49dc3 ("md: convert to kvmalloc") uses kvmalloc_array()
> to allocate memory with GFP_NOIO flag in resize_chunks() via function
> scribble_alloc(),
> 2269 err = scribble_alloc(percpu, new_disks,
> 2270 new_sectors / STRIPE_SECTORS,
> 2271 GFP_NOIO);
>
> The purpose of GFP_NOIO flag to kvmalloc_array() is to allocate
> non-physically continuous pages and avoid extra I/Os of page reclaim
> which triggered by memory allocation. When system memory is under
> heavy pressure, non-physically continuous pages allocation is more
> probably to success than allocating physically continuous pages.
>
> But as a non GFP_KERNEL compatible flag, GFP_NOIO is not acceptible
> by kvmalloc_node() and the memory allocation indeed is handled with
> kmalloc_node() to allocate physically continuous pages. This is not
> the expected behavior of the original purpose when mistakenly using
> GFP_NOIO flag.
>
> In this patch, the memalloc scope APIs memalloc_noio_save() and
> memalloc_noio_restore() are used when calling scribble_alloc(). Then
> when calling kvmalloc_array() with GFP_KERNEL mask, the scope APIs
> may indicatet the allocating context to avoid memory reclaim related
> I/Os, to avoid recursive I/O deadlock on the md raid array itself
> which is calling scribble_alloc() to allocate non-physically continuous
> pages.
>
> This patch also removes gfp_t flags from scribble_alloc() parameters
> list, because the invalid GFP_NOIO is replaced by memalloc scope APIs.
>
> Fixes: b330e6a49dc3 ("md: convert to kvmalloc")
> Signed-off-by: Coly Li <colyli@xxxxxxx>
> Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> ---
> drivers/md/raid5.c | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index ba00e9877f02..6b23f8aba169 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -2228,14 +2228,15 @@ static int grow_stripes(struct r5conf *conf, int num)
> * of the P and Q blocks.
> */
I noticed the comment before scribble_alloc() is outdated. Maybe
fix also that as we are on it?
> static int scribble_alloc(struct raid5_percpu *percpu,
> - int num, int cnt, gfp_t flags)
> + int num, int cnt)
> {
> size_t obj_size =
> sizeof(struct page *) * (num+2) +
> sizeof(addr_conv_t) * (num+2);
> void *scribble;
> + unsigned int noio_flag;
I think we don't use noio_flag in scribble_alloc()?
Thanks,
Song
