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From: Jaewon Kim <jaewon31.kim@samsung.com>
To: Minchan Kim <minchan@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>
Cc: mgorman@suse.de, m.szyprowski@samsung.com, mina86@mina86.com,
	shli@fb.com, akpm@linux-foundation.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com,
	ytk.lee@samsung.com
Subject: Re: [PATCH v2] mm/vmscan: count layzfree pages and fix nr_isolated_* mismatch
Date: Fri, 24 Apr 2020 13:16:45 +0900	[thread overview]
Message-ID: <5EA2682D.7010307@samsung.com> (raw)
In-Reply-To: <20200423200020.GB46847@google.com>



On 2020년 04월 24일 05:00, Minchan Kim wrote:
> On Thu, Apr 23, 2020 at 12:05:46PM -0400, Johannes Weiner wrote:
>> On Thu, Apr 23, 2020 at 12:16:02PM +0900, Jaewon Kim wrote:
>>>
>>> On 2020년 04월 22일 22:07, Johannes Weiner wrote:
>>>> On Wed, Apr 22, 2020 at 05:48:15PM +0900, Jaewon Kim wrote:
>>>>> @@ -1295,11 +1295,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>>>>>  		 */
>>>>>  		if (page_mapped(page)) {
>>>>>  			enum ttu_flags flags = ttu_flags | TTU_BATCH_FLUSH;
>>>>> +			bool lazyfree = PageAnon(page) && !PageSwapBacked(page);
>>>>>  
>>>>>  			if (unlikely(PageTransHuge(page)))
>>>>>  				flags |= TTU_SPLIT_HUGE_PMD;
>>>>> +
>>>>>  			if (!try_to_unmap(page, flags)) {
>>>>>  				stat->nr_unmap_fail += nr_pages;
>>>>> +				if (lazyfree && PageSwapBacked(page))
>>>> This looks pretty strange, until you remember that try_to_unmap()
>>>> could SetPageSwapbacked again.
>>>>
>>>> This might be more obvious?
>>>>
>>>> 			was_swapbacked = PageSwapBacked(page);
>>>> 			if (!try_to_unmap(page, flags)) {
>>>> 				stat->nr_unmap_fail += nr_pages;
>>>> 				if (!was_swapbacked && PageSwapBacked(page))
>>> Hello Johannes, thank you for your comment.
>>>
>>> The name can changed from layzyfree to was_swapbacked.
>>> By the way, did you mean removing PageAnon(page), too? It seems to be OK, though.
>> I can't decide whether PageAnon() makes it clearer or not. But it's
>> not really needed for correctness. So feel free to keep what you had.
> Yub, PageAnon is redundant.
>
>> I would really just at least change bool lazyfree to was_lazyfree,
> It's better.
Thank you both.

Sorry but let me ask again.

Because PageAnon is redundant, let me remove it on checking lazyfree.
Then, I think, was_swapbacked (first suggestion) is better then was_lazyfree (second suggestion),
because it just checks PageSwapBacked(page). And we knows was_swapbacked is used for lazyfree on stat->nr_lazyfree_fail.

If you don't mind let me pick was_swapbacked instead of was_lazyfree
bool was_lazyfree = PageSwapBacked(page);

Thank you

>
>



  reply	other threads:[~2020-04-24  4:16 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20200422084832epcas1p333225f9b6a00c9ce36f5f5d63fe6e3bf@epcas1p3.samsung.com>
2020-04-22  8:48 ` Jaewon Kim
2020-04-22 13:07   ` Johannes Weiner
2020-04-23  3:16     ` Jaewon Kim
2020-04-23 16:05       ` Johannes Weiner
2020-04-23 20:00         ` Minchan Kim
2020-04-24  4:16           ` Jaewon Kim [this message]
2020-04-24 13:17             ` Johannes Weiner

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