Messages in this thread | | | Date | Wed, 12 Nov 2008 13:11:12 +0200 | From | Izik Eidus <> | Subject | Re: [PATCH 2/4] Add replace_page(), change the mapping of pte from one page into another |
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Avi Kivity wrote: > KAMEZAWA Hiroyuki wrote: >> Can I make a question ? (I'm working for memory cgroup.) >> >> Now, we do charge to anonymous page when >> - charge(+1) when it's mapped firstly (mapcount 0->1) >> - uncharge(-1) it's fully unmapped (mapcount 1->0) vir >> page_remove_rmap(). >> >> My quesion is >> - PageKSM pages are not necessary to be tracked by memory cgroup ? When we reaplacing page using page_replace() we have: oldpage - > anonymous page that is going to be replaced by newpage newpage -> kernel allocated page (KsmPage) so about oldpage we are calling page_remove_rmap() that will notify cgroup and about newpage it wont be count inside cgroup beacuse it is file rmap page (we are calling to page_add_file_rmap), so right now PageKSM wont ever be tracked by cgroup.
>> - Can we know that "the page is just replaced and we don't necessary >> to do >> charge/uncharge".
The caller of page_replace does know it, the only problem is that page_remove_rmap() automaticly change the cgroup for anonymous pages, if we want it not to change the cgroup, we can: increase the cgroup count before page_remove (but in that case what happen if we reach to the limit???) give parameter to page_remove_rmap() that we dont want the cgroup to be changed.
>> - annonymous page from KSM is worth to be tracked by memory cgroup ? >> (IOW, it's on LRU and can be swapped-out ?)
KSM have no anonymous pages (it share anonymous pages into KsmPAGE -> kernel allocated page without mapping) so it isnt in LRU and it cannt be swapped, only when KsmPAGEs will be break by do_wp_page() the duplication will be able to swap.
>> > > My feeling is that shared pages should be accounted as if they were > not shared; that is, a share page should be accounted for each process > that shares it. Perhaps sharing within a cgroup should be counted as > 1 page for all the ptes pointing to it. > >
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