Messages in this thread Patch in this message | | | Date | Wed, 20 Jan 2010 09:48:13 +0000 | From | Mel Gorman <> | Subject | Re: [PATCH 5/7] Add /proc trigger for memory compaction |
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On Thu, Jan 07, 2010 at 02:00:16PM -0800, David Rientjes wrote: > On Wed, 6 Jan 2010, Mel Gorman wrote: > > > This patch adds a proc file /proc/sys/vm/compact_node. When a NID is written > > to the file, each zone in that node is compacted. This should be done with > > debugfs but this was what was available to rebase quickly and I suspect > > debugfs either did not exist or was in development during the first > > implementation. > > > > If this interface is to exist in the long term, it needs to be thought > > about carefully. For the moment, it's handy to have to test compaction > > under a controlled setting. > > > > With Lee's work on mempolicy-constrained hugepage allocations, there is a > use-case for this explicit trigger to be exported via sysfs in the > longterm:
True, although the per-node structures are only available on NUMA making it necessary to have two interfaces. The per-node one is handy enough because it would be just
/sys/devices/system/node/nodeX/compact_node When written to, this node is compacted by the writing process
But there does not appear to be a "good" way of having a non-NUMA interface. /sys/devices/system/node does not exist .... Does anyone remember why !NUMA does not have a /sys/devices/system/node/node0? Is there a good reason or was there just no point?
> we should be able to determine how successful the allocation of > hugepages will be on a particular node without actually allocating them > depending on the degree of external fragmentation to form our mempolicy.
You can guess to some extent but can't know without scanning the pages. A simple guess would be based on the number of MIGRATE_MOVABLE pageblocks and the number of LRU pages that are in the node. Something like;
1. Count how many MIGRATE_MOVABLE pageblocks there currently are in the zone (examination of a bitmap)
2. Assuming there is little or no mixing of pageblocks (because min_free_kbytes was tuned properly), calculate how many MIGRATE_MOVABLE pageblocks are required for all the LRU pages in the zone
3. The number of possible hugepages is the difference in the two pageblock counts.
> Since node-targeted hugepage allocation and freeing now exists in the > kernel and compaction is used primary for the former, I don't see why it > shouldn't be exposed. > > I like the (slightly racy) interface that avoids having a trigger for each > node under /sys/devices/system/node as well. >
So, would you be happy with a proc-interface like this and also having a sysfs-based trigger for NUMA? Or do we need to come up with a sysfs-based trigger that works for both NUMA and !NUMA?
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie> > > --- > > include/linux/compaction.h | 5 ++++ > > kernel/sysctl.c | 11 +++++++++ > > mm/compaction.c | 52 ++++++++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 68 insertions(+), 0 deletions(-) > > > > diff --git a/include/linux/compaction.h b/include/linux/compaction.h > > index 6201371..5965ef2 100644 > > --- a/include/linux/compaction.h > > +++ b/include/linux/compaction.h > > @@ -5,4 +5,9 @@ > > #define COMPACT_INCOMPLETE 0 > > #define COMPACT_COMPLETE 1 > > > > +#ifdef CONFIG_MIGRATION > > +extern int sysctl_compaction_handler(struct ctl_table *table, int write, > > + void __user *buffer, size_t *length, loff_t *ppos); > > +#endif /* CONFIG_MIGRATION */ > > + > > #endif /* _LINUX_COMPACTION_H */ > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > > index 8a68b24..6202e95 100644 > > --- a/kernel/sysctl.c > > +++ b/kernel/sysctl.c > > @@ -50,6 +50,7 @@ > > #include <linux/ftrace.h> > > #include <linux/slow-work.h> > > #include <linux/perf_event.h> > > +#include <linux/compaction.h> > > > > #include <asm/uaccess.h> > > #include <asm/processor.h> > > @@ -80,6 +81,7 @@ extern int pid_max; > > extern int min_free_kbytes; > > extern int pid_max_min, pid_max_max; > > extern int sysctl_drop_caches; > > +extern int sysctl_compact_node; > > extern int percpu_pagelist_fraction; > > extern int compat_log; > > extern int latencytop_enabled; > > @@ -1109,6 +1111,15 @@ static struct ctl_table vm_table[] = { > > .mode = 0644, > > .proc_handler = drop_caches_sysctl_handler, > > }, > > +#ifdef CONFIG_MIGRATION > > + { > > + .procname = "compact_node", > > + .data = &sysctl_compact_node, > > + .maxlen = sizeof(int), > > + .mode = 0644, > > This should only need 0200? > > > + .proc_handler = sysctl_compaction_handler, > > + }, > > +#endif /* CONFIG_MIGRATION */ > > { > > .procname = "min_free_kbytes", > > .data = &min_free_kbytes, > > diff --git a/mm/compaction.c b/mm/compaction.c > > index d36760a..a8bcae2 100644 > > --- a/mm/compaction.c > > +++ b/mm/compaction.c > > @@ -11,6 +11,7 @@ > > #include <linux/migrate.h> > > #include <linux/compaction.h> > > #include <linux/mm_inline.h> > > +#include <linux/sysctl.h> > > #include "internal.h" > > > > /* > > @@ -338,3 +339,54 @@ static int compact_zone(struct zone *zone, struct compact_control *cc) > > return ret; > > } > > > > +/* Compact all zones within a node */ > > +int compact_node(int nid) > > +{ > > + int zoneid; > > + pg_data_t *pgdat; > > + struct zone *zone; > > + > > + if (nid < 0 || nid > nr_node_ids || !node_online(nid)) > > + return -EINVAL; > > + pgdat = NODE_DATA(nid); > > + > > + /* Flush pending updates to the LRU lists */ > > + lru_add_drain_all(); > > + > > + printk(KERN_INFO "Compacting memory in node %d\n", nid); > > + for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { > > + struct compact_control cc; > > + > > + zone = &pgdat->node_zones[zoneid]; > > + if (!populated_zone(zone)) > > + continue; > > + > > + cc.nr_freepages = 0; > > + cc.nr_migratepages = 0; > > + cc.zone = zone; > > + INIT_LIST_HEAD(&cc.freepages); > > + INIT_LIST_HEAD(&cc.migratepages); > > + > > + compact_zone(zone, &cc); > > + > > + VM_BUG_ON(!list_empty(&cc.freepages)); > > + VM_BUG_ON(!list_empty(&cc.migratepages)); > > + } > > + printk(KERN_INFO "Compaction of node %d complete\n", nid); > > If it's exposed through sysfs, the printk's should probably be demoted to > pr_debug(). >
I deleted them altogether. The point originally was to measure how long compaction took. It can just as easily be done by running
time echo 0 > compact_node
Thanks > > + > > + return 0; > > +} > > + > > +/* This is global and fierce ugly but it's straight-forward */ > > +int sysctl_compact_node; > > + > > +/* This is the entry point for compacting nodes via /proc/sys/vm */ > > +int sysctl_compaction_handler(struct ctl_table *table, int write, > > + void __user *buffer, size_t *length, loff_t *ppos) > > +{ > > + proc_dointvec(table, write, buffer, length, ppos); > > + if (write) > > + return compact_node(sysctl_compact_node); > > + > > + return 0; > > +} >
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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