From: Ric Mason <ric.masonn@gmail.com>
To: Li Haifeng <omycle@gmail.com>
Cc: Hugh Dickins <hughd@google.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: Should a swapped out page be deleted from swap cache?
Date: Wed, 06 Mar 2013 19:04:10 +0800 [thread overview]
Message-ID: <513722AA.2030001@gmail.com> (raw)
In-Reply-To: <CAFNq8R5ni4jKRsHJLyGiNPcj4epz8q5zva_0XEJrL1-uVZHb9w@mail.gmail.com>
On 03/06/2013 01:34 PM, Li Haifeng wrote:
> 2013/2/20 Ric Mason <ric.masonn@gmail.com>:
>> Hi Hugh,
>>
>>
>> On 02/20/2013 02:56 AM, Hugh Dickins wrote:
>>> On Tue, 19 Feb 2013, Ric Mason wrote:
>>>> There is a call of try_to_free_swap in function swap_writepage, if
>>>> swap_writepage is call from shrink_page_list path, PageSwapCache(page) ==
>>>> trure, PageWriteback(page) maybe false, page_swapcount(page) == 0, then
>>>> will
>>>> delete the page from swap cache and free swap slot, where I miss?
>>> That's correct. PageWriteback is sure to be false there. page_swapcount
>>> usually won't be 0 there, but sometimes it will be, and in that case we
>>> do want to delete from swap cache and free the swap slot.
>>
>> 1) If PageSwapCache(page) == true, PageWriteback(page) == false,
>> page_swapcount(page) == 0 in swap_writepage(shrink_page_list path), then
>> will delete the page from swap cache and free swap slot, in function
>> swap_writepage:
>>
>> if (try_to_free_swap(page)) {
>> unlock_page(page);
>> goto out;
>> }
>> writeback will not execute, that's wrong. Where I miss?
> when the page is deleted from swap cache and corresponding swap slot
> is free, the page is set dirty. The dirty page won't be reclaimed. It
> is not wrong.
I don't think so. For dirty pages, there are two steps: 1)writeback
2)reclaim. Since PageSwapCache(page) == true && PageWriteback(page) ==
false && page_swapcount(page) == 0 in swap_writeback(),
try_to_free_swap() will return true and writeback will be skip. Then how
can step one be executed?
>
> corresponding path lists as below.
> when swap_writepage() is called by pageout() in shrink_page_list().
> pageout() will return PAGE_SUCCESS. For PAGE_SUCCESS, when
> PageDirty(page) is true, this reclaiming page will be keeped in the
> inactive LRU list.
> shrink_page_list()
> {
> ...
> 904 switch (pageout(page, mapping, sc)) {
> 905 case PAGE_KEEP:
> 906 nr_congested++;
> 907 goto keep_locked;
> 908 case PAGE_ACTIVATE:
> 909 goto activate_locked;
> 910 case PAGE_SUCCESS:
> 911 if (PageWriteback(page))
> 912 goto keep_lumpy;
> 913 if (PageDirty(page))
> 914 goto keep;
> ...}
>
>> 2) In the function pageout, page will be set PG_Reclaim flag, since this
>> flag is set, end_swap_bio_write->end_page_writeback:
>> if (TestClearPageReclaim(page))
>> rotate_reclaimable_page(page);
>> it means that page will be add to the tail of lru list, page is clean
>> anonymous page this time and will be reclaim to buddy system soon, correct?
> correct
>> If is correct, what is the meaning of rotate here?
> Rotating here is to add the page to the tail of inactive LRU list. So
> this page will be reclaimed ASAP while reclaiming.
>
>>> Hugh
>>
next prev parent reply other threads:[~2013-03-06 11:04 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-18 10:48 Should a swapped out page be deleted from swap cache? Li Haifeng
2013-02-18 18:06 ` Hugh Dickins
2013-02-19 0:39 ` Will Huck
2013-02-19 19:06 ` Hugh Dickins
2013-02-20 0:43 ` Will Huck
2013-02-19 2:04 ` Li Haifeng
2013-02-19 2:38 ` Will Huck
2013-02-19 6:53 ` Li Haifeng
2013-02-19 9:38 ` Sha Zhengju
2013-02-19 18:49 ` Hugh Dickins
2013-02-19 8:32 ` Ric Mason
2013-02-19 18:56 ` Hugh Dickins
2013-02-20 0:40 ` Ric Mason
2013-03-06 5:34 ` Li Haifeng
2013-03-06 11:04 ` Ric Mason [this message]
2013-03-06 11:10 ` Ric Mason
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