linux-kernel - Re: [PATCH 2/5] mm/debug_pagealloc: don't allocate page

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Message-ID: <7391d520-0512-231b-ef2d-600ab22bda5b@suse.cz>
Date:	Thu, 11 Aug 2016 11:53:18 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:	Minchan Kim <minchan@...nel.org>, Michal Hocko <mhocko@...nel.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 2/5] mm/debug_pagealloc: don't allocate page_ext if we
 don't use guard page

On 08/10/2016 08:16 AM, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> What debug_pagealloc does is just mapping/unmapping page table.
> Basically, it doesn't need additional memory space to memorize something.
> But, with guard page feature, it requires additional memory to distinguish
> if the page is for guard or not. Guard page is only used when
> debug_guardpage_minorder is non-zero so this patch removes additional
> memory allocation (page_ext) if debug_guardpage_minorder is zero.
>
> It saves memory if we just use debug_pagealloc and not guard page.

We could also save cycles with a static key for _debug_guardpage_enabled :)

But memory savings are likely more significant, so

> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>