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    SubjectRe: [RFC][PATCH 5/5] (experimental) chase and free cache only swap
    On Wed, 27 May 2009 15:30:24 +0900
    Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

    > On Wed, 27 May 2009 14:14:42 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > > On Tue, 26 May 2009 12:18:34 +0900
    > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > >
    > > >
    > > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > > >
    > > This is a replacement for this. (just an idea, not testd.)
    > >
    > > I think this works well. Does anyone has concerns ?
    > I think so too, except some trivial build errors ;)
    >
    Oh, will be fixed in the next post :(

    > I'll test it, but it will take a long time to see the effect of this patch
    > even if setting the swap space to reasonable size.
    >
    Yes, Hot-to-test is my concern, too..

    Thanks,
    -Kame


    >
    > Thanks,
    > Daisuke Nishimura.
    >
    > > Do I have to modify swap-cluster code to do this in sane way ?
    > >
    > > ---
    > > mm/swapfile.c | 40 ++++++++++++++++++++++++++++++++++++++++
    > > 1 file changed, 40 insertions(+)
    > >
    > > Index: new-trial-swapcount/mm/swapfile.c
    > > ===================================================================
    > > --- new-trial-swapcount.orig/mm/swapfile.c
    > > +++ new-trial-swapcount/mm/swapfile.c
    > > @@ -74,6 +74,26 @@ static inline unsigned short make_swap_c
    > > return ret;
    > > }
    > >
    > > +static int try_to_reuse_swap(struct swap_info_struct *si, unsigned long offset)
    > > +{
    > > + int type = si - swap_info;
    > > + swp_entry_t entry = swp_entry(type, offset);
    > > + struct page *page;
    > > +
    > > + page = find_get_page(page);
    > > + if (!page)
    > > + return 0;
    > > + if (!trylock_page(page)) {
    > > + page_cache_release(page);
    > > + return 0;
    > > + }
    > > + try_to_free_swap(page);
    > > + unlock_page(page);
    > > + page_cache_release(page);
    > > + return 1;
    > > +}
    > > +
    > > +
    > > /*
    > > * We need this because the bdev->unplug_fn can sleep and we cannot
    > > * hold swap_lock while calling the unplug_fn. And swap_lock
    > > @@ -295,6 +315,18 @@ checks:
    > > goto no_page;
    > > if (offset > si->highest_bit)
    > > scan_base = offset = si->lowest_bit;
    > > +
    > > + /* reuse swap entry of cache-only swap if not busy. */
    > > + if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
    > > + int ret;
    > > + spin_unlock(&swap_lock);
    > > + ret = try_to_reuse_swap(si, offset));
    > > + spin_lock(&swap_lock);
    > > + if (ret)
    > > + goto checks; /* we released swap_lock */
    > > + goto scan;
    > > + }
    > > +
    > > if (si->swap_map[offset])
    > > goto scan;
    > >
    > > @@ -378,6 +410,10 @@ scan:
    > > spin_lock(&swap_lock);
    > > goto checks;
    > > }
    > > + if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
    > > + spin_lock(&swap_lock);
    > > + goto checks;
    > > + }
    > > if (unlikely(--latency_ration < 0)) {
    > > cond_resched();
    > > latency_ration = LATENCY_LIMIT;
    > > @@ -389,6 +425,10 @@ scan:
    > > spin_lock(&swap_lock);
    > > goto checks;
    > > }
    > > + if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
    > > + spin_lock(&swap_lock);
    > > + goto checks;
    > > + }
    > > if (unlikely(--latency_ration < 0)) {
    > > cond_resched();
    > > latency_ration = LATENCY_LIMIT;
    > >
    >



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