linux-kernel - Re: [PATCH] mm, memcg: sync allocation and memcg charge gfp flags for THP

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Date:	Wed, 18 Mar 2015 16:59:05 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, memcg: sync allocation and memcg charge gfp flags
 for THP

On Wed 18-03-15 16:40:34, Vlastimil Babka wrote:
> On 03/18/2015 04:02 PM, Michal Hocko wrote:
> >On Wed 18-03-15 15:34:50, Vlastimil Babka wrote:
> >>On 03/16/2015 03:08 PM, Michal Hocko wrote:
> >>>@@ -1080,6 +1080,7 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
> >>>  	unsigned long haddr;
> >>>  	unsigned long mmun_start;	/* For mmu_notifiers */
> >>>  	unsigned long mmun_end;		/* For mmu_notifiers */
> >>>+	gfp_t huge_gfp = GFP_TRANSHUGE;	/* for allocation and charge */
> >>
> >>This value is actually never used. Is it here because the compiler emits a
> >>spurious non-initialized value warning otherwise? It should be easy for it
> >>to prove that setting new_page to something non-null implies initializing
> >>huge_gfp (in the hunk below), and NULL new_page means it doesn't reach the
> >>mem_cgroup_try_charge() call?
> >
> >No, I haven't tried to workaround the compiler. It just made the code
> >more obvious to me. I can remove the initialization if you prefer, of
> >course.
> 
> Yeah IMHO it would be better to remove it, if possible. Leaving it has the
> (albeit small) chance that future patch will again use the value in the code
> before it's determined based on defrag setting.
 
Wouldn't an uninitialized value be used in such a case?

-- 
Michal Hocko
SUSE Labs
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