lkml.org 
[lkml]   [2014]   [Sep]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH v3 1/4] mm/page_alloc: fix incorrect isolation behavior by rechecking migratetype
On 09/15/2014 04:31 AM, Joonsoo Kim wrote:
> On Mon, Sep 08, 2014 at 10:31:29AM +0200, Vlastimil Babka wrote:
>> On 08/26/2014 10:08 AM, Joonsoo Kim wrote:
>>
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index f86023b..51e0d13 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -740,9 +740,15 @@ static void free_one_page(struct zone *zone,
>>> if (nr_scanned)
>>> __mod_zone_page_state(zone, NR_PAGES_SCANNED, -nr_scanned);
>>>
>>> + if (unlikely(has_isolate_pageblock(zone))) {
>>> + migratetype = get_pfnblock_migratetype(page, pfn);
>>> + if (is_migrate_isolate(migratetype))
>>> + goto skip_counting;
>>> + }
>>> + __mod_zone_freepage_state(zone, 1 << order, migratetype);
>>> +
>>> +skip_counting:
>>
>> Here, wouldn't a simple 'else __mod_zone_freepage_state...' look
>> better than goto + label? (same for the following 2 patches). Or
>> does that generate worse code?
>
> To remove goto label, we need two __mod_zone_freepage_state() like
> as below. On my system, it doesn't generate worse code, but, I am not
> sure that this is true if more logic would be added. I think that
> goto + label is better.

Oh right, I missed that. It's a bit subtle, but I don't see a nicer
solution right now.

> + if (unlikely(has_isolate_pageblock(zone))) {
> + migratetype = get_pfnblock_migratetype(page, pfn);
> + if (!is_migrate_isolate(migratetype))
> + __mod_zone_freepage_state(zone, 1 << order, migratetype);
> + } else {
> + __mod_zone_freepage_state(zone, 1 << order, migratetype);
> }
>

Yeah that would be uglier I guess.

> Anyway, What do you think which one is better, either v2 or v3? Still, v3? :)

Yeah v3 is much better than v1 was, and better for backporting than v2.
The changelogs also look quite clear. The overhead shouldn't be bad with
the per-zone flag guarding get_pfnblock_migratetype.

I'm just not sure about patch 4 and potentially leaving unmerged budies
behind. How would it look if instead we made sure isolation works on
whole MAX_ORDER blocks instead?

Vlastimil

> Thanks.
>



\
 
 \ /
  Last update: 2014-09-24 16:01    [W:0.069 / U:0.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site