On 2016/1/30 3:25, ChengYi He wrote:
> While buddy system fallbacks to allocate different migration type pages,
> it prefers the largest feasible pages and might split the chosen page
> into smalller ones. If the largest feasible pages are less than or equal
> to orde-3 and migration fallback happens frequently, then order-2 and
> order-3 pages can be exhausted easily. This patch aims to allocate the
> smallest feasible pages for the fallback mechanism under this condition.
>
> Signed-off-by: ChengYi He <chengyihetaipei@xxxxxxxxx>
> ---
> mm/page_alloc.c | 19 ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 50c325a..3fcb653 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1802,9 +1802,22 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
> struct page *page;
>
> /* Find the largest possible block of pages in the other list */
> - for (current_order = MAX_ORDER-1;
> - current_order >= order && current_order <= MAX_ORDER-1;
> - --current_order) {
> + for (current_order = MAX_ORDER - 1;
> + current_order >= max_t(unsigned int, PAGE_ALLOC_COSTLY_ORDER + 1, order);
> + --current_order) {
> + page = __rmqueue_fallback_order(zone, order, start_migratetype,
> + current_order);
> +
> + if (page)
> + return page;
> + }
> +
> + /*
> + * While current_order <= PAGE_ALLOC_COSTLY_ORDER, find the smallest
> + * feasible pages in the other list to avoid splitting high order pages
> + */
> + for (current_order = order; current_order <= PAGE_ALLOC_COSTLY_ORDER;
> + ++current_order) {
> page = __rmqueue_fallback_order(zone, order, start_migratetype,
> current_order);
>
Hi Chengyi,
So you mean use the largest block first, if no large block left, the use the
smallest block, right?
I have an idea, how about set two migrate types(movable and unmovable) when
doing init work? The function is memmap_init_zone().
I don't know how to set the ratio, maybe unmovable takes 1/10 memory, and left
9/10 memory to movable? I think this effect is a little like the two zones
(normal and movable).
Another two ideas
https://lkml.org/lkml/2015/8/14/67
7d348b9ea64db0a315d777ce7d4b06697f946503, maybe this patch is not applied on your 3.10
Thanks,
Xishi Qiu
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