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SubjectRe: [PATCH -mm 11/25] more aggressively use lumpy reclaim
On Fri, 06 Jun 2008 16:28:49 -0400
Rik van Riel <riel@redhat.com> wrote:

> From: Rik van Riel <riel@redhat.com>
>
> During an AIM7 run on a 16GB system, fork started failing around
> 32000 threads, despite the system having plenty of free swap and
> 15GB of pageable memory.

Can we upadte the changelog to explain why this actually happened?

>From reading the patch I _assume_ that

a) the kernel was using 8k (2-page) stacks and

b) all the memory was stuck on the active list, so reclaim wasn't
able to find any order-1 pages and wasn't able to find any order-0
pages which gave it allocatable order-1 pages.

?

> If normal pageout does not result in contiguous free pages for
> kernel stacks, fall back to lumpy reclaim instead of failing fork
> or doing excessive pageout IO.

hm, I guess that this para kinda says that. Not sure what the
"excessive pageout IO" part is referring to?

> I do not know whether this change is needed due to the extreme
> stress test or because the inactive list is a smaller fraction
> of system memory on huge systems.
>

I guess that tweaking the inactive_ratio could be used to determine
this?

>
> ---
> mm/vmscan.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> Index: linux-2.6.26-rc2-mm1/mm/vmscan.c
> ===================================================================
> --- linux-2.6.26-rc2-mm1.orig/mm/vmscan.c 2008-05-28 12:14:34.000000000 -0400
> +++ linux-2.6.26-rc2-mm1/mm/vmscan.c 2008-05-28 12:14:43.000000000 -0400
> @@ -857,7 +857,8 @@ int isolate_lru_page(struct page *page)
> * of reclaimed pages
> */
> static unsigned long shrink_inactive_list(unsigned long max_scan,
> - struct zone *zone, struct scan_control *sc, int file)
> + struct zone *zone, struct scan_control *sc,
> + int priority, int file)
> {
> LIST_HEAD(page_list);
> struct pagevec pvec;
> @@ -875,8 +876,19 @@ static unsigned long shrink_inactive_lis
> unsigned long nr_freed;
> unsigned long nr_active;
> unsigned int count[NR_LRU_LISTS] = { 0, };
> - int mode = (sc->order > PAGE_ALLOC_COSTLY_ORDER) ?
> - ISOLATE_BOTH : ISOLATE_INACTIVE;
> + int mode = ISOLATE_INACTIVE;
> +
> + /*
> + * If we need a large contiguous chunk of memory, or have
> + * trouble getting a small set of contiguous pages, we
> + * will reclaim both active and inactive pages.
> + *
> + * We use the same threshold as pageout congestion_wait below.
> + */
> + if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
> + mode = ISOLATE_BOTH;
> + else if (sc->order && priority < DEF_PRIORITY - 2)
> + mode = ISOLATE_BOTH;
>
> nr_taken = sc->isolate_pages(sc->swap_cluster_max,
> &page_list, &nr_scan, sc->order, mode,
> @@ -1171,7 +1183,7 @@ static unsigned long shrink_list(enum lr
> shrink_active_list(nr_to_scan, zone, sc, priority, file);
> return 0;
> }
> - return shrink_inactive_list(nr_to_scan, zone, sc, file);
> + return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
> }



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