2011/6/23 Michal Hocko <mhocko@xxxxxxx>:
> On Thu 23-06-11 22:01:40, Hiroyuki Kamezawa wrote:
>> 2011/6/23 Michal Hocko <mhocko@xxxxxxx>:
>> > On Thu 23-06-11 19:01:57, KAMEZAWA Hiroyuki wrote:
>> >> On Thu, 23 Jun 2011 11:02:04 +0200
>> >> Michal Hocko <mhocko@xxxxxxx> wrote:
>> >>
>> >> > On Thu 23-06-11 17:08:11, KAMEZAWA Hiroyuki wrote:
>> >> > > On Thu, 23 Jun 2011 09:41:33 +0200
>> >> > > Michal Hocko <mhocko@xxxxxxx> wrote:
>> >> > [...]
>> >> > > > Other than that:
>> >> > > > Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
>> >> > > >
>> >> > >
>> >> > > I found the page is added to LRU before charging. (In this case,
>> >> > > memcg's LRU is ignored.) I'll post a new version with a fix.
>> >> >
>> >> > Yes, you are right. I have missed that.
>> >> > This means that we might race with reclaim which could evict the COWed
>> >> > page wich in turn would uncharge that page even though we haven't
>> >> > charged it yet.
>> >> >
>> >> > Can we postpone page_add_new_anon_rmap to the charging path or it would
>> >> > just race somewhere else?
>> >> >
>> >>
>> >> I got a different idea. How about this ?
>> >> I think this will have benefit for non-memcg users under OOM, too.
>> >
>> > Could you be more specific? I do not see how preallocation which might
>> > turn out to be pointless could help under OOM.
>> >
>>
>> We'll have no page allocation under lock_page() held in this path.
>> I think it is good.
>
> But it can also cause that the page, we are about to fault in, is evicted
> due to allocation so we would have to do a major fault... This is
> probably not that serious, though.
For other purpose, I have(had) other patch to prevent it (and planned
to post it.)
The basic logic is...
1. add a new member variable to vm_area_struct as
vma->vm_faulting_to
2. at __do_fault(), set vm_faulting_to as
vma->vm_faulting_to = pgoff.
3. chec vma->vm_faulting_to at page_referenced_file() as
if (pgoff (Was page->index) == vma->vm_faulting_to)
referenced++
Then, the page which someone is waiting for page-fault will be marked as
referenced and go KEEP_LOCKED.
(vm_faulting_to can be cleared after we got lock_page()).
In corner case, several threads which shares vma may fault into a vma.
But this will help typical case and have no overheads, I think.
Thanks,
-Kame
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