Messages in this thread | | | Date | Tue, 21 Apr 2009 18:23:31 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [patch 3/3][rfc] vmscan: batched swap slot allocation |
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On Tue, 21 Apr 2009 10:52:31 +0200 Johannes Weiner <hannes@cmpxchg.org> wrote:
> > Keeping multiple pages locked while they stay on private list ? > > Yeah, it's a bit suboptimal but I don't see a way around it. > Hmm, seems to increase stale swap cache dramatically under memcg ;)
> > BTW, isn't it better to add "allocate multiple swap space at once" function > > like > > - void get_swap_pages(nr, swp_entry_array[]) > > ? "nr" will not be bigger than SWAP_CLUSTER_MAX. > > It will sometimes be, see __zone_reclaim(). > Hm ? If I read the code correctly, __zone_reclaim() just call shrink_zone() and "nr" to shrink_page_list() is SWAP_CLUSTER_MAX, at most.
> I had such a function once. The interesting part is: how and when do > you call it? If you drop the page lock in between, you need to redo > the checks for unevictability and whether the page has become mapped > etc. > > You also need to have the pages in swap cache as soon as possible or > optimistic swap-in will 'steal' your swap slots. See add_to_swap() > when the cache radix tree says -EEXIST. >
If I was you, modify "offset" calculation of get_swap_pages() -> scan_swap_map() to allow that a cpu tends to find countinous swap page cluster. Too difficult ?
Regards, -Kame
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