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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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