Hi, The original message is somehow determined to be junk mail and rejected by the system. Forward this message. ---------- Forwarded message ---------- From: Wenwei Tao <ww.tao0320@xxxxxxxxx> Date: 2016-06-19 10:40 GMT+08:00 Subject: Re: [RFC PATCH 1/3] mm, page_alloc: free HIGHATOMIC page directly to the allocator To: Vlastimil Babka <vbabka@xxxxxxx> 抄送: Wenwei Tao <wwtao0320@xxxxxxx>, akpm@xxxxxxxxxxxxxxxxxxxx, mgorman@xxxxxxxxxxxxxxxxxxx, mhocko@xxxxxxxx, rientjes@xxxxxxxxxx, kirill.shutemov@xxxxxxxxxxxxxxx, iamjoonsoo.kim@xxxxxxx, izumi.taku@xxxxxxxxxxxxxx, Johannes Weiner <hannes@xxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx 2016-06-18 18:14 GMT+08:00 Vlastimil Babka <vbabka@xxxxxxx>: > On 06/18/2016 11:34 AM, Wenwei Tao wrote: >> From: Wenwei Tao <ww.tao0320@xxxxxxxxx> >> >> Some pages might have already been allocated before reserve >> the pageblock as HIGHATOMIC. When free these pages, put them >> directly to the allocator instead of the pcp lists since they >> might have the chance to be merged to high order pages. > > Are there some data showing the improvement, or just theoretical? > It's just theoretical. I read the mm code and try to understand it, think this might be an optimization. >> Signed-off-by: Wenwei Tao <ww.tao0320@xxxxxxxxx> >> --- >> mm/page_alloc.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 6903b69..19f9e76 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -2412,7 +2412,8 @@ void free_hot_cold_page(struct page *page, bool cold) > > The full comment that's here for context: > > /* > * We only track unmovable, reclaimable and movable on pcp lists. > * Free ISOLATE pages back to the allocator because they are being > * offlined but treat RESERVE as movable pages so we can get those > * areas back if necessary. Otherwise, we may have to free > * excessively into the page allocator > */ > > That comment looks outdated as it refers to RESERVE, which was replaced > by HIGHATOMIC. But there's some reasoning why these pages go to > pcplists. I'd expect the "free excessively" part isn't as bad as > highatomic reserves are quite limited. They also shouldn't be used for > order-0 allocations, which is what this function is about, so I would > expect both the impact on "free excessively" and the improvement of > merging to be minimal? > >> * excessively into the page allocator >> */ >> if (migratetype >= MIGRATE_PCPTYPES) { >> - if (unlikely(is_migrate_isolate(migratetype))) { >> + if (unlikely(is_migrate_isolate(migratetype) || >> + migratetype == MIGRATE_HIGHATOMIC)) { >> free_one_page(zone, page, pfn, 0, migratetype); >> goto out; >> } > > In any case your patch highlighted that this code could be imho > optimized like below. > > if (unlikely(migratetype >= MIGRATE_PCPTYPES)) > if (is_migrate_cma(migratetype)) { > migratetype = MIGRATE_MOVABLE; > } else { > free_one_page(zone, page, pfn, 0, migratetype); > goto out; > } > } > > That's less branches than your patch, and even less than originally if > CMA is not enabled (or with ZONE_CMA). Yeah, this looks better. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href