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

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Date:	Tue, 24 Nov 2015 15:42:49 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Kyeongdon Kim <kyeongdon.kim@....com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH 2/3] zram: try vmalloc() after kmalloc()

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...):

---

 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)
--
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