lkml.org 
[lkml]   [2018]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] mm: thp: fix potential clearing to referenced flag in page_idle_clear_pte_refs_one()
From
Date


On 2/8/18 8:33 PM, Kirill A. Shutemov wrote:
> On Thu, Feb 08, 2018 at 02:39:26PM -0800, Andrew Morton wrote:
>> On Tue, 6 Feb 2018 08:06:36 +0800 Yang Shi <yang.shi@linux.alibaba.com> wrote:
>>
>>> For PTE-mapped THP, the compound THP has not been split to normal 4K
>>> pages yet, the whole THP is considered referenced if any one of sub
>>> page is referenced.
>>>
>>> When walking PTE-mapped THP by pvmw, all relevant PTEs will be checked
>>> to retrieve referenced bit. But, the current code just returns the
>>> result of the last PTE. If the last PTE has not referenced, the
>>> referenced flag will be cleared.
>>>
>>> So, here just break pvmw walk once referenced PTE is found if the page
>>> is a part of THP.
>>>
>>> ...
>>>
>>> --- a/mm/page_idle.c
>>> +++ b/mm/page_idle.c
>>> @@ -67,6 +67,14 @@ static bool page_idle_clear_pte_refs_one(struct page *page,
>>> if (pvmw.pte) {
>>> referenced = ptep_clear_young_notify(vma, addr,
>>> pvmw.pte);
>>> + /*
>>> + * For PTE-mapped THP, one sub page is referenced,
>>> + * the whole THP is referenced.
>>> + */
>>> + if (referenced && PageTransCompound(pvmw.page)) {
>>> + page_vma_mapped_walk_done(&pvmw);
>>> + break;
>>> + }
>> This means that the function will no longer clear the referenced bits
>> in all the ptes. What effect does this have and should we document
>> this in some fashion?
> Yeah, the patch is wrong. We need to get all ptes for THP cleared.
>
> What about something like this instead (untested):

Thanks, Kirill. It looks correct. All ptes should be cleared.

I'm going to prepare v2 patch.

Regards,
Yang

>
> diff --git a/mm/page_idle.c b/mm/page_idle.c
> index 0a49374e6931..6876522c9dce 100644
> --- a/mm/page_idle.c
> +++ b/mm/page_idle.c
> @@ -65,10 +65,10 @@ static bool page_idle_clear_pte_refs_one(struct page *page,
> while (page_vma_mapped_walk(&pvmw)) {
> addr = pvmw.address;
> if (pvmw.pte) {
> - referenced = ptep_clear_young_notify(vma, addr,
> + referenced |= ptep_clear_young_notify(vma, addr,
> pvmw.pte);
> } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
> - referenced = pmdp_clear_young_notify(vma, addr,
> + referenced |= pmdp_clear_young_notify(vma, addr,
> pvmw.pmd);
> } else {
> /* unexpected pmd-mapped page? */

\
 
 \ /
  Last update: 2018-02-09 05:48    [W:0.054 / U:41.852 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site