Messages in this thread | | | Date | Thu, 4 Jun 2009 14:57:33 +0900 | From | Daisuke Nishimura <> | Subject | Re: [PATCH 3/4] reuse unused swap entry if necessary |
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On Tue, 2 Jun 2009 12:12:02 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > > This is a replacement for > mm-reuse-unused-swap-entry-if-necessary.patch in mmotm. > function is renamed and comments are added. > > == > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > Now, we can know the swap is just used as SwapCache via swap_map, > without looking up swap cache. > > Then, we have a chance to reuse swap-cache-only swap entries in > get_swap_pages(). > > This patch tries to free swap-cache-only swap entries if swap is > not enough. > Note: We hit following path when swap_cluster code cannot find > a free cluster. Then, vm_swap_full() is not only condition to allow > the kernel to reclaim unused swap. > > Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
I've confirmed that usage increase of swap and swapcache stopped at some threshold in my test, in which , before this patch, some programs had been oom-killed after a long time because of shortage of swap space.
This has been merged to mm already though:
Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Thanks, Daiuske Nishimura.
> --- > mm/swapfile.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 47 insertions(+) > > Index: mmotm-2.6.30-May28/mm/swapfile.c > =================================================================== > --- mmotm-2.6.30-May28.orig/mm/swapfile.c > +++ mmotm-2.6.30-May28/mm/swapfile.c > @@ -79,6 +79,32 @@ static inline unsigned short encode_swap > return ret; > } > > +/* returnes 1 if swap entry is freed */ > +static int > +__try_to_reclaim_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; > + int ret = 0; > + > + page = find_get_page(&swapper_space, entry.val); > + if (!page) > + return 0; > + /* > + * This function is called from scan_swap_map() and it's called > + * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here. > + * We have to use trylock for avoiding deadlock. This is a special > + * case and you should use try_to_free_swap() with explicit lock_page() > + * in usual operations. > + */ > + if (trylock_page(page)) { > + ret = try_to_free_swap(page); > + unlock_page(page); > + } > + page_cache_release(page); > + return ret; > +} > > /* > * We need this because the bdev->unplug_fn can sleep and we cannot > @@ -301,6 +327,19 @@ 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 swap_was_freed; > + spin_unlock(&swap_lock); > + swap_was_freed = __try_to_reclaim_swap(si, offset); > + spin_lock(&swap_lock); > + /* entry was freed successfully, try to use this again */ > + if (swap_was_freed) > + goto checks; > + goto scan; /* check next one */ > + } > + > if (si->swap_map[offset]) > goto scan; > > @@ -382,6 +421,10 @@ 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; > @@ -393,6 +436,10 @@ 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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