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

Sergey Senozhatsky
2022-11-24T03:32:59Z

On (22/11/22 12:30), Sergey Senozhatsky 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. The same applies to zswap_writeback_entry().
>
> Use GFP_KERNEL for temporary buffer allocation in both
> cases.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Nhat Pham <nphamcs@gmail.com>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> ---

Folks, how do we want to proceed with this? One of the hunks here
conflicts with https://lore.kernel.org/lkml/20221119001536.2086599-2-nphamcs@gmail.com/

Do we want to remove conflicting hunk from "[PATCH 1/6] zswap: fix writeback
lock ordering for zsmalloc" and pick this patch up?

> diff --git a/mm/zpool.c b/mm/zpool.c
> index 68facc193496..f46c0d5e766c 100644
> --- a/mm/zpool.c
> +++ b/mm/zpool.c
> @@ -387,6 +387,13 @@ bool zpool_evictable(struct zpool *zpool)
> * zpool_can_sleep_mapped - Test if zpool can sleep when do mapped.
> * @zpool: The zpool to test
> *
> + * Some allocators enter non-preemptible context in ->map() callback (e.g.
> + * disable pagefaults) and exit that context in ->unmap(), which limits what
> + * we can do with the mapped object. For instance, we cannot wait for
> + * asynchronous crypto API to decompress such an object or take mutexes
> + * since those will call into the scheduler. This function tells us whether
> + * we use such an allocator.
> + *
> * Returns: true if zpool can sleep; false otherwise.
> */
> bool zpool_can_sleep_mapped(struct zpool *zpool)
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 2d48fd59cc7a..3019f0bde194 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -958,7 +958,7 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
> };
>
> if (!zpool_can_sleep_mapped(pool)) {
> - tmp = kmalloc(PAGE_SIZE, GFP_ATOMIC);
> + tmp = kmalloc(PAGE_SIZE, GFP_KERNEL);
> if (!tmp)
> return -ENOMEM;
> }
> @@ -1311,7 +1311,7 @@ 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;
> --
> 2.38.1.584.g0f3c55d4c2-goog
>