linux-kernel - Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was "zram: do not use copy

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Message-ID: <20170419061149.GD2881@jagdpanzerIV.localdomain>
Date:   Wed, 19 Apr 2017 15:11:49 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Minchan Kim <minchan@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was
 "zram: do not use copy_page with non-page alinged address")

On (04/18/17 13:06), Michal Hocko wrote:
[..]
> > > copy_page is a performance sensitive function and I believe that we do
> > > those tricks exactly for this purpose.
> > 
> > a wild thought,
> > 
> > use
> > 	#define copy_page(to,from)	memcpy((to), (from), PAGE_SIZE)
> > 
> > when DEBUG_SLAB is set? so arch copy_page() (if provided by arch)
> > won't be affected otherwise.
> 
> SLAB is not guaranteed to provide page size aligned object AFAIR.

oh, if there are no guarantees for page_sized allocations regardless
the .config then agree, won't help.

	-ss