linux-kernel - Re: [PATCH 06/10] ksm: identify PageKsm pages

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Date:	Tue, 21 Jul 2009 13:55:13 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	Izik Eidus <ieidus@...hat.com>, akpm@...ux-foundation.org,
	hugh.dickins@...cali.co.uk, chrisw@...hat.com, avi@...hat.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	nickpiggin@...oo.com.au, Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [PATCH 06/10] ksm: identify PageKsm pages

Andrea Arcangeli wrote:

>> +static inline void page_add_ksm_rmap(struct page *page)
>> +{
>> +	if (atomic_inc_and_test(&page->_mapcount)) {
>> +		page->mapping = (void *) PAGE_MAPPING_ANON;
>> +		__inc_zone_page_state(page, NR_ANON_PAGES);
>> +	}
>> +}
> 
> Is it correct to account them as anon pages?

Yes, but ...

>> -	if (PageAnon(old_page)) {
>> +	if (PageAnon(old_page) && !PageKsm(old_page)) {
>>  		if (!trylock_page(old_page)) {
>>  			page_cache_get(old_page);
>>  			pte_unmap_unlock(page_table, ptl);
> 
> What exactly does it buy to have PageAnon return 1 on ksm pages,
> besides requiring the above additional check (that if we stick to the
> above code, I would find safer to move inside reuse_swap_page).

I guess that if they are to remain unswappable, they
should go onto the unevictable list.

Then again, I'm guessing this is all about to change
in not too much time :)

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