Messages in this thread | | | Date | Thu, 11 Jul 2013 10:02:48 +0900 | From | Joonsoo Kim <> | Subject | Re: [RFC PATCH 1/5] mm, page_alloc: support multiple pages allocation |
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On Wed, Jul 10, 2013 at 03:52:42PM -0700, Dave Hansen wrote: > On 07/03/2013 01:34 AM, Joonsoo Kim wrote: > > - if (page) > > + do { > > + page = buffered_rmqueue(preferred_zone, zone, order, > > + gfp_mask, migratetype); > > + if (!page) > > + break; > > + > > + if (!nr_pages) { > > + count++; > > + break; > > + } > > + > > + pages[count++] = page; > > + if (count >= *nr_pages) > > + break; > > + > > + mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK]; > > + if (!zone_watermark_ok(zone, order, mark, > > + classzone_idx, alloc_flags)) > > + break; > > + } while (1); > > I'm really surprised this works as well as it does. Calling > buffered_rmqueue() a bunch of times enables/disables interrupts a bunch > of times, and mucks with the percpu pages lists a whole bunch. > buffered_rmqueue() is really meant for _single_ pages, not to be called > a bunch of times in a row. > > Why not just do a single rmqueue_bulk() call?
Hello, Dave.
There are some reasons why I implement the feature in this way.
rmqueue_bulk() needs a zone lock. If we allocate not so many pages, for example, 2 or 3 pages, it can have much more overhead rather than allocationg 1 page multiple times. So, IMHO, it is better that multiple pages allocation is supported on top of percpu pages list.
And I think that enables/disables interrupts a bunch of times help to avoid a latency problem. If we disable interrupts until the whole works is finished, interrupts can be handled too lately. free_hot_cold_page_list() already do enables/disalbed interrupts a bunch of times.
Thanks for helpful comment!
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