Messages in this thread | | | Date | Wed, 27 May 2009 16:15:35 -0700 | From | Andrew Morton <> | Subject | Re: [patch] mm: release swap slots for actively used pages |
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On Wed, 27 May 2009 03:47:39 +0200 Johannes Weiner <hannes@cmpxchg.org> wrote:
> For anonymous pages activated by the reclaim scan or faulted from an > evicted page table entry we should always try to free up swap space. > > Both events indicate that the page is in active use and a possible > change in the working set. Thus removing the slot association from > the page increases the chance of the page being placed near its new > LRU buddies on the next eviction and helps keeping the amount of stale > swap cache entries low. > > try_to_free_swap() inherently only succeeds when the last user of the > swap slot vanishes so it is safe to use from places where that single > mapping just brought the page back to life. >
Seems that this has a risk of worsening swap fragmentation for some situations. Or not, I have no way of knowing, really.
> diff --git a/mm/memory.c b/mm/memory.c > index 8b4e40e..407ebf7 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2671,8 +2671,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma, > mem_cgroup_commit_charge_swapin(page, ptr); > > swap_free(entry); > - if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page)) > - try_to_free_swap(page); > + try_to_free_swap(page); > unlock_page(page); > > if (write_access) { > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 621708f..2f0549d 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -788,7 +788,7 @@ cull_mlocked: > > activate_locked: > /* Not a candidate for swapping, so reclaim swap space. */ > - if (PageSwapCache(page) && vm_swap_full()) > + if (PageSwapCache(page)) > try_to_free_swap(page); > VM_BUG_ON(PageActive(page)); > SetPageActive(page);
How are we to know that this is a desirable patch for Linux??
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