linux-kernel - Re: [PATCH v2 3/3] zram: pass gfp from zcomp frontend to backend

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Date:	Fri, 27 Nov 2015 11:30:53 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Kyeongdon Kim <kyeongdon.kim@....com>,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH v2 3/3] zram: pass gfp from zcomp frontend to backend

On (11/27/15 11:19), Sergey Senozhatsky wrote:
[..]
> > > +static struct zcomp_strm *zcomp_strm_alloc(struct zcomp *comp, gfp_t flags)
> > >  {
> > > +               zstrm = zcomp_strm_alloc(comp, GFP_NOIO|__GFP_NORETRY|
> > > +                                       __GFP_NOWARN|__GFP_NOMEMALLOC);
> > 
> > 
> > and it seems that after 3/3 (v2) we also lost GFP_ZERO for private
> > allocation. kzalloc->kmalloc, and no explicit __GFP_ZERO for __vmalloc().
> > 
> 
> well, we probably don't really need __GFP_ZERO for ->private, but
> let's address it in a separate patch, not as an undocumented change.

hm... something like this perhaps. I don't think there any security
issues with removing __GFP_ZERO, we have 'garbage' in ->private anyway.


    zram/zcomp: do not zero out zcomp private pages
    
    Do not __GFP_ZERO allocated zcomp ->private pages. We keep
    allocated streams around and use them for read/write requests,
    so we supply a zeroed out ->private to compression algorithm
    as a scratch buffer only once -- the first time we use that
    stream. For the rest of IO requests served by this stream
    ->private usually contains some temporarily data from the
    previous requests.

---

diff --git a/drivers/block/zram/zcomp_lz4.c b/drivers/block/zram/zcomp_lz4.c
index dc2338d..0110086 100644
--- a/drivers/block/zram/zcomp_lz4.c
+++ b/drivers/block/zram/zcomp_lz4.c
@@ -19,10 +19,10 @@ static void *zcomp_lz4_create(gfp_t flags)
 {
        void *ret;
 
-       ret = kzalloc(LZ4_MEM_COMPRESS, flags);
+       ret = kmalloc(LZ4_MEM_COMPRESS, flags);
        if (!ret)
                ret = __vmalloc(LZ4_MEM_COMPRESS,
-                               flags | __GFP_ZERO | __GFP_HIGHMEM,
+                               flags | __GFP_HIGHMEM,
                                PAGE_KERNEL);
        return ret;
 }
diff --git a/drivers/block/zram/zcomp_lzo.c b/drivers/block/zram/zcomp_lzo.c
index 0ab6fce..ed7a1f0 100644
--- a/drivers/block/zram/zcomp_lzo.c
+++ b/drivers/block/zram/zcomp_lzo.c
@@ -19,10 +19,10 @@ static void *lzo_create(gfp_t flags)
 {
        void *ret;
 
-       ret = kzalloc(LZO1X_MEM_COMPRESS, flags);
+       ret = kmalloc(LZO1X_MEM_COMPRESS, flags);
        if (!ret)
                ret = __vmalloc(LZO1X_MEM_COMPRESS,
-                               flags | __GFP_ZERO | __GFP_HIGHMEM,
+                               flags | __GFP_HIGHMEM,
                                PAGE_KERNEL);
        return ret;
 }
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