Re: [PATCH] zswap: do not allocate from atomic pool

Andrew Morton
2022-11-22T01:56:25Z

On Tue, 22 Nov 2022 10:33:38 +0900 Sergey Senozhatsky <senozhatsky@chromium.org> wrote:

> zswap_frontswap_load() should be called from preemptible
> context (we even call mutex_lock() there) and it does not
> look like we need to do GFP_ATOMIC allocaion for temp
> buffer there. Use GFP_KERNEL instead.
>
> ...
>
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1314,7 +1314,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> }
>
> if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
> - tmp = kmalloc(entry->length, GFP_ATOMIC);
> + tmp = kmalloc(entry->length, GFP_KERNEL);
> if (!tmp) {
> ret = -ENOMEM;
> goto freeentry;

It seems strange to do

if (! can sleep)
do something which can sleep

or am I misreading the intent of zpool_driver.sleep_mapped? If so,
perhaps some explanatory code comments will help.