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SubjectRe: [PATCH 2/9] ksm: let shared pages be swappable
On Tue, 24 Nov 2009 16:42:15 +0000 (GMT)
Hugh Dickins <hugh.dickins@tiscali.co.uk> wrote:
> +int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
> + unsigned long *vm_flags)
> +{
> + struct stable_node *stable_node;
> + struct rmap_item *rmap_item;
> + struct hlist_node *hlist;
> + unsigned int mapcount = page_mapcount(page);
> + int referenced = 0;
> + struct vm_area_struct *vma;
> +
> + VM_BUG_ON(!PageKsm(page));
> + VM_BUG_ON(!PageLocked(page));
> +
> + stable_node = page_stable_node(page);
> + if (!stable_node)
> + return 0;
> +

Hmm. I'm not sure how many pages are shared in a system but
can't we add some threshold for avoidng too much scan against shared pages ?
(in vmscan.c)
like..

if (page_mapcount(page) > (XXXX >> scan_priority))
return 1;

I saw terrible slow downs in shmem-swap-out in old RHELs (at user support).
(Added kosaki to CC.)

After this patch, the number of shared swappable page will be unlimited.

Thanks,
-Kame




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