Re: + zram-use-gfp_kernel-for-post-processing-slot-allocation.patch added to mm-new branch

[Sergey Senozhatsky <senozhatsky@chromium.org>]

On (26/03/05 17:49), Andrew Morton wrote:
> 
> The patch titled
>      Subject: zram: use GFP_KERNEL for post-processing slot allocation
> has been added to the -mm mm-new branch.  Its filename is
>      zram-use-gfp_kernel-for-post-processing-slot-allocation.patch
> 
> This patch will shortly appear at
>      https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-use-gfp_kernel-for-post-processing-slot-allocation.patch

[..]

> 
> Post-processing slot allocation used to be performed under slot bit-lock,
> so gfp was restricted, then we switched to a sleepable slot lock but gpf
> still remained restricted.  Drop that restriction and use GFP_KERNEL
> instead.
> 
> Link: https://lkml.kernel.org/r/20260305021619.617481-1-senozhatsky@chromium.org
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Acked-by: Brian Geffon <bgeffon@google.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Minchan Kim <minchan@kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  drivers/block/zram/zram_drv.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/drivers/block/zram/zram_drv.c~zram-use-gfp_kernel-for-post-processing-slot-allocation
> +++ a/drivers/block/zram/zram_drv.c
> @@ -297,7 +297,7 @@ static bool place_pp_slot(struct zram *z
>  	struct zram_pp_slot *pps;
>  	u32 bid;
>  
> -	pps = kmalloc_obj(*pps, GFP_NOIO | __GFP_NOWARN);
> +	pps = kmalloc_obj(*pps, GFP_KERNEL | __GFP_NOWARN);
>  	if (!pps)
>  		return false;

Right... that was silly.
Andrew, can you please drop this patch?  We cannot reclaim memory
in place_pp_slot(), because it's called under slot-lock, which is
IO lock for zram.  We cannot re-enter zram under IO lock, so we have
to keep using GFP_NOIO here.