linux-kernel - Re: [PATCH 2/3] zram: try vmalloc() after kmalloc()

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Message-ID: <20151124070814.GC7708@blaptop>
Date:	Tue, 24 Nov 2015 16:08:14 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Kyeongdon Kim <kyeongdon.kim@....com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH 2/3] zram: try vmalloc() after kmalloc()

On Tue, Nov 24, 2015 at 03:42:49PM +0900, Sergey Senozhatsky wrote:
> On (11/24/15 15:12), Sergey Senozhatsky wrote:
> > [..]
> > >  static void *zcomp_lz4_create(void)
> > >  {
> > > -       return kzalloc(LZ4_MEM_COMPRESS, GFP_KERNEL);
> > > +       void *ret;
> > > +
> > > +       /*
> > > +        * This function could be called in swapout/fs write path
> > > +        * so we couldn't use GFP_FS|IO. And it assumes we already
> > > +        * have at least one stream in zram initialization so we
> > > +        * don't do best effort to allocate more stream in here.
> > > +        * A default stream will work well without further multiple
> > > +        * stream. That's why we use  __GFP_NORETRY|NOWARN|NOMEMALLOC.
> > > +        */
> > > +       ret = kzalloc(LZ4_MEM_COMPRESS,
> > > +                       __GFP_NORETRY|__GFP_NOWARN|__GFP_NOMEMALLOC);
> > > +       if (!ret)
> > > +               ret = __vmalloc(LZ4_MEM_COMPRESS,
> > > +                                       __GFP_NORETRY|__GFP_NOWARN|
> > > +                                       __GFP_NOMEMALLOC|__GFP_ZERO,
> > > +                                       PAGE_KERNEL);
> > > +       return ret;
> > >  }
> > [..]
> > 
> > so this change is still questionable. is there a real value in having
> > a vmalloc() fallback in the middle of allocations sequence:
> > 
> > 	zstrm = kmalloc(sizeof(*zstrm), GFP_NOIO);
> > 		^^^ ok, can fail here
> > 
> 
> oh, and by the way, we still can get a warning from this guy. so NOWARN in
> ->create() only is not enough, should be propogated to zstrm alloc too.
> so is __get_free_pages() (that was not in the original patch).
> 
> so pass nowarn everywhere.
> 
> perhaps something like (__GFP_NORETRY... hm...):

Yep. zcomp_strm_alloc has several allocation side and they have used
different flags so in our discussion, there are a few time mistakes to
miss so I want to pass gfp_t from client to zcomp_strm_alloc and
all of allocation sites in zcomp_strm_alloc use the flag consistenly
like my [3/3].

Thanks.

> 
> ---
> 
>  drivers/block/zram/zcomp.c     | 6 ++++--
>  drivers/block/zram/zcomp_lz4.c | 3 ++-
>  drivers/block/zram/zcomp_lzo.c | 3 ++-
>  3 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> index c536177..c0d02d5 100644
> --- a/drivers/block/zram/zcomp.c
> +++ b/drivers/block/zram/zcomp.c
> @@ -76,7 +76,8 @@ 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_NOIO);
> +	struct zcomp_strm *zstrm = kmalloc(sizeof(*zstrm), GFP_NOIO |
> +			__GFP_NORETRY | __GFP_NOWARN | __GFP_NOMEMALLOC);
>  	if (!zstrm)
>  		return NULL;
>  
> @@ -85,7 +86,8 @@ 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_NOIO | __GFP_ZERO, 1);
> +	zstrm->buffer = (void *)__get_free_pages(GFP_NOIO | __GFP_NOWARN |
> +			__GFP_ZERO, 1);
>  	if (!zstrm->private || !zstrm->buffer) {
>  		zcomp_strm_free(comp, zstrm);
>  		zstrm = NULL;
> diff --git a/drivers/block/zram/zcomp_lz4.c b/drivers/block/zram/zcomp_lz4.c
> index ee44b51..dbeee93 100644
> --- a/drivers/block/zram/zcomp_lz4.c
> +++ b/drivers/block/zram/zcomp_lz4.c
> @@ -15,7 +15,8 @@
>  
>  static void *zcomp_lz4_create(void)
>  {
> -	return kzalloc(LZ4_MEM_COMPRESS, GFP_NOIO);
> +	return kzalloc(LZ4_MEM_COMPRESS, GFP_NOIO | __GFP_NORETRY |
> +			__GFP_NOWARN | __GFP_NOMEMALLOC);
>  }
>  
>  static void zcomp_lz4_destroy(void *private)
> diff --git a/drivers/block/zram/zcomp_lzo.c b/drivers/block/zram/zcomp_lzo.c
> index 683ce04..19c0857 100644
> --- a/drivers/block/zram/zcomp_lzo.c
> +++ b/drivers/block/zram/zcomp_lzo.c
> @@ -15,7 +15,8 @@
>  
>  static void *lzo_create(void)
>  {
> -	return kzalloc(LZO1X_MEM_COMPRESS, GFP_NOIO);
> +	return kzalloc(LZO1X_MEM_COMPRESS, GFP_NOIO | __GFP_NORETRY |
> +			__GFP_NOWARN | __GFP_NOMEMALLOC);
>  }
>  
>  static void lzo_destroy(void *private)

-- 
Kind regards,
Minchan Kim
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