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 <[email protected]> > --- > 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
