Re: [PATCH] zram/zcomp: use GFP_NOIO to allocate streams

Andrew Morton
2015-11-23T23:18:15Z

On Mon, 23 Nov 2015 22:27:59 +0900 Sergey Senozhatsky <sergey.senozhatsky@gmail.com> wrote:

> We can end up allocating a new compression stream with GFP_KERNEL
> from within the IO path, which may result is nested (recursive) IO
> operations. That can introduce problems if the IO path in question
> is a reclaimer, holding some locks that will deadlock nested IOs.
>
> Allocate streams and working memory using GFP_NOIO flag, forbidding
> recursive IO and FS operations.
>
> ...
>
> --- a/drivers/block/zram/zcomp.c
> +++ b/drivers/block/zram/zcomp.c
> @@ -76,7 +76,7 @@ static void zcomp_strm_free(struct zcomp *comp, struct zcomp_strm *zstrm)
> */
> static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
> {
> - struct zcomp_strm *zstrm = kmalloc(sizeof(*zstrm), GFP_KERNEL);
> + struct zcomp_strm *zstrm = kmalloc(sizeof(*zstrm), GFP_NOIO);
> if (!zstrm)
> return NULL;
>
> @@ -85,7 +85,7 @@ static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp)
> * allocate 2 pages. 1 for compressed data, plus 1 extra for the
> * case when compressed size is larger than the original one
> */
> - zstrm->buffer = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
> + zstrm->buffer = (void *)__get_free_pages(GFP_NOIO | __GFP_ZERO, 1);

OK.

> --- a/drivers/block/zram/zcomp_lz4.c
> +++ b/drivers/block/zram/zcomp_lz4.c
> @@ -20,10 +20,13 @@ static void *zcomp_lz4_create(void)
> void *ret;
>
> ret = kzalloc(LZ4_MEM_COMPRESS,
> - __GFP_NORETRY|__GFP_NOWARN|__GFP_NOMEMALLOC);
> - if (!ret)
> - ret = vzalloc(LZ4_MEM_COMPRESS);
> - return ret;
> + __GFP_NORETRY | __GFP_NOWARN | __GFP_NOMEMALLOC);

But here we've still lost __GFP_RECLAIM, unnecessarily. And it's quite
unclear why __GFP_NORETRY and __GFP_NOMEMALLOC are being used.

IOW, why not simply use (GFP_NOIO|__GFP_NOWARN)?