linux-kernel - Re: [PATCH 2/6] mm, hwpoison: use __PageMovable() to detect non-lru movable pages

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Date:   Mon, 5 Sep 2022 14:53:41 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] mm, hwpoison: use __PageMovable() to detect non-lru
 movable pages

On 2022/9/5 13:22, HORIGUCHI NAOYA(堀口 直也) wrote:
> Hi Miaohe,
> 
> On Tue, Aug 30, 2022 at 08:36:00PM +0800, Miaohe Lin wrote:
>> It's more recommended to use __PageMovable() to detect non-lru movable
>> pages. We can avoid bumping page refcnt via isolate_movable_page() for
>> the isolated lru pages. Also if pages become PageLRU just after they're
>> checked but before trying to isolate them, isolate_lru_page() will be
>> called to do the right work.
> 
> Good point, non-lru movable page is currently handled by isolate_lru_page(),
> which always fails.  This means that we lost the chance of soft-offlining
> for any non-lru movable page.  So this patch improves the situation.

Non-lru movable page will still be handled by isolate_movable_page() before the code change
as they don't have PageLRU set. The current situation is that the isolated LRU pages are
passed to isolate_movable_page() uncorrectly. This might not hurt. But the chance that pages
become un-isolated and thus available just after checking could be seized with this patch.

> 
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> ---
>>  mm/memory-failure.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>> index a923a6dde871..3966fa6abe03 100644
>> --- a/mm/memory-failure.c
>> +++ b/mm/memory-failure.c
>> @@ -2404,7 +2404,7 @@ EXPORT_SYMBOL(unpoison_memory);
>>  static bool isolate_page(struct page *page, struct list_head *pagelist)
>>  {
>>  	bool isolated = false;
>> -	bool lru = PageLRU(page);
>> +	bool lru = !__PageMovable(page);
> 
> It seems that PAGE_MAPPING_MOVABLE is not set for hugetlb pages, so
> lru becomes true for them.  Then, if isolate_hugetlb() succeeds,
> inc_node_page_state() is called for hugetlb pages, maybe that's not expected.

Yes, that's unexpected. Thanks for pointing this out.

> 
>>  
>>  	if (PageHuge(page)) {
>>  		isolated = !isolate_hugetlb(page, pagelist);
>         } else {
>                 if (lru)
>                         isolated = !isolate_lru_page(page);
>                 else
>                         isolated = !isolate_movable_page(page, ISOLATE_UNEVICTABLE);
> 
>                 if (isolated)
>                         list_add(&page->lru, pagelist);
>         }
> 
>         if (isolated && lru)
>                 inc_node_page_state(page, NR_ISOLATED_ANON +
>                                     page_is_file_lru(page));
> 
> so, how about moving this if block into the above else block?
> Then, the automatic variable lru can be moved into the else block.

Do you mean something like below?

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index df3bf266eebf..48780f3a61d3 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2404,24 +2404,25 @@ EXPORT_SYMBOL(unpoison_memory);
 static bool isolate_page(struct page *page, struct list_head *pagelist)
 {
        bool isolated = false;
-       bool lru = !__PageMovable(page);

        if (PageHuge(page)) {
                isolated = !isolate_hugetlb(page, pagelist);
        } else {
+               bool lru = !__PageMovable(page);
+
                if (lru)
                        isolated = !isolate_lru_page(page);
                else
                        isolated = !isolate_movable_page(page, ISOLATE_UNEVICTABLE);

-               if (isolated)
+               if (isolated) {
                        list_add(&page->lru, pagelist);
+                       if (lru)
+                               inc_node_page_state(page, NR_ISOLATED_ANON +
+                                                   page_is_file_lru(page));
+               }
        }

-       if (isolated && lru)
-               inc_node_page_state(page, NR_ISOLATED_ANON +
-                                   page_is_file_lru(page));
-
        /*
         * If we succeed to isolate the page, we grabbed another refcount on
         * the page, so we can safely drop the one we got from get_any_pages().

> 
> Thanks,
> Naoya Horiguchi

Thanks a lot for your review and comment on this series, Naoya.

Thanks,
Miaohe Lin.