linux-kernel - Re: [PATCH V4 3/4] mm: reduce try_to_compact

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Message-ID: <54ACFA9A.8000405@suse.cz>
Date:	Wed, 07 Jan 2015 10:21:30 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Michal Hocko <mhocko@...e.cz>
CC:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	Minchan Kim <minchan@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH V4 3/4] mm: reduce try_to_compact_pages parameters

On 01/07/2015 10:18 AM, Michal Hocko wrote:
> On Wed 07-01-15 10:11:45, Vlastimil Babka wrote:
>> On 01/06/2015 03:57 PM, Michal Hocko wrote:
>> > Hmm, wait a minute
>> > 
>> > On Mon 05-01-15 18:17:42, Vlastimil Babka wrote:
>> > [...]
>> >> -unsigned long try_to_compact_pages(struct zonelist *zonelist,
>> >> -			int order, gfp_t gfp_mask, nodemask_t *nodemask,
>> >> -			enum migrate_mode mode, int *contended,
>> >> -			int alloc_flags, int classzone_idx)
>> >> +unsigned long try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
>> >> +			int alloc_flags, const struct alloc_context *ac,
>> >> +			enum migrate_mode mode, int *contended)
>> >>  {
>> >> -	enum zone_type high_zoneidx = gfp_zone(gfp_mask);
>> >>  	int may_enter_fs = gfp_mask & __GFP_FS;
>> >>  	int may_perform_io = gfp_mask & __GFP_IO;
>> >>  	struct zoneref *z;
>> > 
>> > gfp_mask might change since the high_zoneidx was set up in the call
>> > chain. I guess this shouldn't change to the gfp_zone output but it is
>> > worth double checking.
>> 
>> Yeah I checked that. gfp_zone() operates just on GFP_ZONEMASK part of the flags,
>> and we don't change that.
> 
> That was my understanding as well. Maybe we want
> VM_BUG_ON(gfp_zone(gfp_mask) != ac->high_zoneidx);

That sounds like an arbitrary overkill to me. I think that gfp_zone() was just
used here to save an extra parameter.
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