From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 14 Feb 2008 12:14:27 -0800 (PST) From: Christoph Lameter Subject: Re: [patch 4/5] slub: Use __GFP_MOVABLE for slabs of HPAGE_SIZE In-Reply-To: <20080214200849.GB30841@csn.ul.ie> Message-ID: References: <20080214040245.915842795@sgi.com> <20080214040314.118141086@sgi.com> <20080214141442.GF17641@csn.ul.ie> <20080214200849.GB30841@csn.ul.ie> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Mel Gorman Cc: Pekka Enberg , Nick Piggin , Andrew Morton , linux-mm@kvack.org List-ID: On Thu, 14 Feb 2008, Mel Gorman wrote: > > Doesnt it mean that the allocations can occur in MAX_ORDER blocks > > marked MOVABLE? > > Blocks aren't MAX_ORDER in size, they are pageblock_order in size and that > value can be thought of as HUGETLB_PAGE_ORDER. No matter what you mark them > as, it is still one pageblock. If you leave them as RECLAIMABLE or UNMOVABLE, > a MOVABLE block may still get reclaimed and given to slab instead without > this patch. Marking them movable when no partition exists gains nothing at all. Ok so order 9 allocs of slub could occur in pageblock_order blocks like what happens for huge pages today. AFAICT this makes the handling of slab pages consistent with huge pages? > > echo 2 >/proc/sys/vm/drop_cache will usually allow a significant shrinkage > > of the slab caches. In many ways it is the same. > > > > Except it doesn't work for all slabs. As part of the highorder allocation > stress tests I run, a final part is allocating pages when no other process is > running and /proc/sys/vm/drop_cache has been used. There are still remaining > pages left in odd places. Nor does it work for huge pages which cannot be moved but they are marked __GFP_MOVABLE anyways. > > This is a feature enabled by a special command line boot option. So its > > something that the admin did *intentionally*. > > Not quite. What he asked for is that slub_min_order=HUGE_PAGESIZE, not > slub_use_zone_movable. In a situation where they wanted to have a hugepage > pool that reliably resized and slub_min_order == HUGE_PAGESIZE, he would > find that they collide for no obvious reason. Hmm.... So they would use the size of the movable area to size the hugetlb area? > > A system with huge amounts of memory has a large amount of huge > > pages. It is typically at this point to have 4G per cpu in a system and we > > may go higher. 4G means up to 2048 huge pages per cpu! Huge page > > allocation will be quite common and its good to reduce page allocator > > overhead. > Marking them movable makes no difference to that assertion. Hmmmm... Okay if pages are managed in pageblock_size chunks that are of HUGE_PAGE_SIZE then this patch makes no difference whatsoever. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org