Re: [PATCH v2 03/20] mm, hugetlb: fix subpool accounting handling

[Aneesh Kumar K.V]

Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> writes:

> On Thu, Aug 22, 2013 at 12:38:12PM +0530, Aneesh Kumar K.V wrote:
>> Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> writes:
>> 
>> > Hello, Aneesh.
>> >
>> > First of all, thank you for review!
>> >
>> > On Wed, Aug 21, 2013 at 02:58:20PM +0530, Aneesh Kumar K.V wrote:
>> >> Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> writes:
>> >> 
>> >> > If we alloc hugepage with avoid_reserve, we don't dequeue reserved one.
>> >> > So, we should check subpool counter when avoid_reserve.
>> >> > This patch implement it.
>> >> 
>> >> Can you explain this better ? ie, if we don't have a reservation in the
>> >> area chg != 0. So why look at avoid_reserve. 
>> >
>> > We don't consider avoid_reserve when chg != 0.
>> > Look at following code.
>> >
>> > +       if (chg || avoid_reserve)
>> > +               if (hugepage_subpool_get_pages(spool, 1))
>> >
>> > It means that if chg != 0, we skip to check avoid_reserve.
>> 
>> when whould be avoid_reserve == 1 and chg == 0 ?
>
> In this case, we should do hugepage_subpool_get_pages(), since we don't
> get a reserved page due to avoid_reserve.

As per off-list discussion we had around this, please add additional
information in commit message explaining when we have
avoid_reserve == 1 and chg == 0

Something like the below copied from call site.

	 /* If the process that created a MAP_PRIVATE mapping is about to
	  * perform a COW due to a shared page count, attempt to satisfy
	  * the allocation without using the existing reserves
          */

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>

-aneesh

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