Cc to linux-mm and hpc guys. and intetionally full quote. > So over the last couple of weeks, I've noticed that our shiny new IMAP > servers (Dual Xeon E5520 + Intel S5520UR MB) with 48G of RAM haven't > been performing as well as expected, and there were some big oddities. > Namely two things stuck out: > > 1. There was free memory. There's 20T of data on these machines. The > kernel should have used lots of memory for caching, but for some > reason, it wasn't. cache ~ 2G, buffers ~ 25G, unused ~ 5G > 2. The machine has an SSD for very hot data. In total, there's about 16G > of data on the SSD. Almost all of that 16G of data should end up > being cached, so there should be little reading from the SSDs at all. > Instead we saw at peak times 2k+ blocks read/s from the SSDs. Again a > sign that caching wasn't working. > > After a bunch of googling, I found this thread. > > http://lkml.org/lkml/2009/5/12/586 > > It appears that patch never went anywhere, and zone_reclaim_mode is > still defaulting to 1 on our pretty standard file/email/web server type > machine with a NUMA kernel. > > By changing it to 0, we saw an immediate massive change in caching > behaviour. Now cache ~ 27G, buffers ~ 7G and unused ~ 0.2G, and IO reads > from the SSD dropped to 100/s instead of 2000/s. > > Having very little knowledge of what this actually does, I'd just > like to point out that from a users point of view, it's really > annoying for your machine to be crippled by a default kernel setting > that's pretty obscure. > > I don't think our usage scenario of serving lots of files is that > uncommon, every file server/email server/web server will be doing pretty > much that and expecting a large part of their memory to be used as a > cache, which clearly isn't what actually happens. > > Rob > Rob Mueller > robm@xxxxxxxxxxx > Yes, sadly intel motherboard turn on zone_reclaim_mode by default. and current zone_reclaim_mode doesn't fit file/web server usecase ;-) So, I've created new proof concept patch. This doesn't disable zone_reclaim at all. Instead, distinguish for file cache and for anon allocation and only file cache doesn't use zone-reclaim. That said, high-end hpc user often turn on cpuset.memory_spread_page and they avoid this issue. But, why don't we consider avoid it by default? Rob, I wonder if following patch help you. Could you please try it? Subject: [RFC] vmscan: file cache doesn't use zone_reclaim by default --- Need to removed debbuging piece. Documentation/sysctl/vm.txt | 7 +++---- fs/inode.c | 2 +- include/linux/gfp.h | 9 +++++++-- include/linux/mmzone.h | 2 ++ include/linux/swap.h | 6 ++++++ mm/filemap.c | 1 + mm/page_alloc.c | 8 +++++++- mm/vmscan.c | 7 ++----- mm/vmstat.c | 2 ++ 9 files changed, 31 insertions(+), 13 deletions(-) diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index b606c2c..4be569e 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -671,16 +671,15 @@ This is value ORed together of 1 = Zone reclaim on 2 = Zone reclaim writes dirty pages out 4 = Zone reclaim swaps pages +8 = Zone reclaim for file cache on zone_reclaim_mode is set during bootup to 1 if it is determined that pages from remote zones will cause a measurable performance reduction. The page allocator will then reclaim easily reusable pages (those page cache pages that are currently not used) before allocating off node pages. -It may be beneficial to switch off zone reclaim if the system is -used for a file server and all of memory should be used for caching files -from disk. In that case the caching effect is more important than -data locality. +By default, for file cache allocation doesn't use zone reclaim. But +It can be turned on manually. Allowing zone reclaim to write out pages stops processes that are writing large amounts of data from dirtying pages on other nodes. Zone diff --git a/fs/inode.c b/fs/inode.c index 8646433..02a51b1 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -166,7 +166,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode) mapping->a_ops = &empty_aops; mapping->host = inode; mapping->flags = 0; - mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE); + mapping_set_gfp_mask(mapping, GFP_FILE_CACHE); mapping->assoc_mapping = NULL; mapping->backing_dev_info = &default_backing_dev_info; mapping->writeback_index = 0; diff --git a/include/linux/gfp.h b/include/linux/gfp.h index 975609c..f263b1f 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h @@ -84,6 +84,10 @@ struct vm_area_struct; #define GFP_HIGHUSER_MOVABLE (__GFP_WAIT | __GFP_IO | __GFP_FS | \ __GFP_HARDWALL | __GFP_HIGHMEM | \ __GFP_MOVABLE) + +#define GFP_FILE_CACHE (GFP_HIGHUSER | __GFP_RECLAIMABLE | __GFP_MOVABLE) + + #define GFP_IOFS (__GFP_IO | __GFP_FS) #ifdef CONFIG_NUMA @@ -120,11 +124,12 @@ struct vm_area_struct; /* Convert GFP flags to their corresponding migrate type */ static inline int allocflags_to_migratetype(gfp_t gfp_flags) { - WARN_ON((gfp_flags & GFP_MOVABLE_MASK) == GFP_MOVABLE_MASK); - if (unlikely(page_group_by_mobility_disabled)) return MIGRATE_UNMOVABLE; + if ((gfp_flags & GFP_MOVABLE_MASK) == GFP_MOVABLE_MASK) + gfp_flags &= ~__GFP_RECLAIMABLE; + /* Group based on mobility */ return (((gfp_flags & __GFP_MOVABLE) != 0) << 1) | ((gfp_flags & __GFP_RECLAIMABLE) != 0); diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 6e6e626..2eead52 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -112,6 +112,8 @@ enum zone_stat_item { NUMA_LOCAL, /* allocation from local node */ NUMA_OTHER, /* allocation from other node */ #endif + NR_ZONE_CACHE_AVOID, + NR_ZONE_RECLAIM, NR_VM_ZONE_STAT_ITEMS }; /* diff --git a/include/linux/swap.h b/include/linux/swap.h index 2fee51a..487bc3b 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -65,6 +65,12 @@ static inline int current_is_kswapd(void) #define MAX_SWAPFILES \ ((1 << MAX_SWAPFILES_SHIFT) - SWP_MIGRATION_NUM - SWP_HWPOISON_NUM) +#define RECLAIM_OFF 0 +#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ +#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ +#define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ +#define RECLAIM_CACHE (1<<3) /* Reclaim even though file cache purpose allocation */ + /* * Magic header for a swap area. The first part of the union is * what the swap magic looks like for the old (limited to 128MB) diff --git a/mm/filemap.c b/mm/filemap.c index 3d4df44..97298c0 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -468,6 +468,7 @@ struct page *__page_cache_alloc(gfp_t gfp) if (cpuset_do_page_mem_spread()) { get_mems_allowed(); n = cpuset_mem_spread_node(); + gfp &= ~__GFP_RECLAIMABLE; page = alloc_pages_exact_node(n, gfp, 0); put_mems_allowed(); return page; diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 8587c10..f81c28f 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1646,9 +1646,15 @@ zonelist_scan: classzone_idx, alloc_flags)) goto try_this_zone; - if (zone_reclaim_mode == 0) + if (zone_reclaim_mode == RECLAIM_OFF) goto this_zone_full; + if (!(zone_reclaim_mode & RECLAIM_CACHE) && + (gfp_mask & GFP_MOVABLE_MASK) == GFP_MOVABLE_MASK) { + inc_zone_state(zone, NR_ZONE_CACHE_AVOID); + goto try_next_zone; + } + ret = zone_reclaim(zone, gfp_mask, order); switch (ret) { case ZONE_RECLAIM_NOSCAN: diff --git a/mm/vmscan.c b/mm/vmscan.c index c391c32..6f63eea 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2558,11 +2558,6 @@ module_init(kswapd_init) */ int zone_reclaim_mode __read_mostly; -#define RECLAIM_OFF 0 -#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ -#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ -#define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ - /* * Priority for ZONE_RECLAIM. This determines the fraction of pages * of a node considered for each zone_reclaim. 4 scans 1/16th of @@ -2646,6 +2641,8 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) }; unsigned long nr_slab_pages0, nr_slab_pages1; + inc_zone_state(zone, NR_ZONE_RECLAIM); + cond_resched(); /* * We need to be able to allocate from the reserves for RECLAIM_SWAP diff --git a/mm/vmstat.c b/mm/vmstat.c index f389168..8988688 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -740,6 +740,8 @@ static const char * const vmstat_text[] = { "numa_local", "numa_other", #endif + "zone_cache_avoid", + "zone_reclaim", #ifdef CONFIG_VM_EVENT_COUNTERS "pgpgin", -- 1.6.5.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>