On Thu 19-03-15 09:57:10, Eric B Munson wrote: > Currently, pages which are marked as unevictable are protected from > compaction, but not from other types of migration. The POSIX real time > extension explicitly states that mlock() will prevent a major page > fault, but the spirit of is is that mlock() should give a process the > ability to control sources of latency, including minor page faults. > However, the mlock manpage only explicitly says that a locked page will > not be written to swap and this can cause some confusion. The > compaction code today, does not give a developer who wants to avoid swap > but wants to have large contiguous areas available any method to achieve > this state. This patch introduces a sysctl for controlling compaction > behavoir with respect to the unevictable lru. Users that demand no page > faults after a page is present can set compact_unevictable to 0 and > users who need the large contiguous areas can enable compaction on > locked memory by leaving the default value of 1. > > To illustrate this problem I wrote a quick test program that mmaps a > large number of 1MB files filled with random data. These maps are > created locked and read only. Then every other mmap is unmapped and I > attempt to allocate huge pages to the static huge page pool. When the > compact_unevictable sysctl is 0, I cannot allocate hugepages after > fragmenting memory. When the value is set to 1, allocations succeed. > > Signed-off-by: Eric B Munson <[email protected]> > Cc: Vlastimil Babka <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Christoph Lameter <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Mel Gorman <[email protected]> > Cc: David Rientjes <[email protected]> > Cc: Rik van Riel <[email protected]> > Cc: Michal Hocko <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected]
Acked-by: Michal Hocko <[email protected]> Thanks! > --- > Changes from V5: > * Default sysctl value is now 1 > * Used more descriptive sysctl name > * documentation calss out default value > > Documentation/sysctl/vm.txt | 11 +++++++++++ > include/linux/compaction.h | 1 + > kernel/sysctl.c | 9 +++++++++ > mm/compaction.c | 7 +++++++ > 4 files changed, 28 insertions(+) > > diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt > index 902b457..9832ec5 100644 > --- a/Documentation/sysctl/vm.txt > +++ b/Documentation/sysctl/vm.txt > @@ -21,6 +21,7 @@ Currently, these files are in /proc/sys/vm: > - admin_reserve_kbytes > - block_dump > - compact_memory > +- compact_unevictable_allowed > - dirty_background_bytes > - dirty_background_ratio > - dirty_bytes > @@ -106,6 +107,16 @@ huge pages although processes will also directly compact > memory as required. > > ============================================================== > > +compact_unevictable_allowed > + > +Available only when CONFIG_COMPACTION is set. When set to 1, compaction is > +allowed to examine the unevictable lru (mlocked pages) for pages to compact. > +This should be used on systems where stalls for minor page faults are an > +acceptable trade for large contiguous free memory. Set to 0 to prevent > +compaction from moving pages that are unevictable. Default value is 1. > + > +============================================================== > + > dirty_background_bytes > > Contains the amount of dirty memory at which the background kernel > diff --git a/include/linux/compaction.h b/include/linux/compaction.h > index a014559..aa8f61c 100644 > --- a/include/linux/compaction.h > +++ b/include/linux/compaction.h > @@ -34,6 +34,7 @@ extern int sysctl_compaction_handler(struct ctl_table > *table, int write, > extern int sysctl_extfrag_threshold; > extern int sysctl_extfrag_handler(struct ctl_table *table, int write, > void __user *buffer, size_t *length, loff_t *ppos); > +extern int sysctl_compact_unevictable_allowed; > > extern int fragmentation_index(struct zone *zone, unsigned int order); > extern unsigned long try_to_compact_pages(gfp_t gfp_mask, unsigned int order, > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 88ea2d6..2f6c880 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -1313,6 +1313,15 @@ static struct ctl_table vm_table[] = { > .extra1 = &min_extfrag_threshold, > .extra2 = &max_extfrag_threshold, > }, > + { > + .procname = "compact_unevictable_allowed", > + .data = &sysctl_compact_unevictable_allowed, > + .maxlen = sizeof(int), > + .mode = 0644, > + .proc_handler = proc_dointvec, > + .extra1 = &zero, > + .extra2 = &one, > + }, > > #endif /* CONFIG_COMPACTION */ > { > diff --git a/mm/compaction.c b/mm/compaction.c > index 8c0d945..ad88a8c 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1047,6 +1047,12 @@ typedef enum { > } isolate_migrate_t; > > /* > + * Allow userspace to control policy on scanning the unevictable LRU for > + * compactable pages. > + */ > +int sysctl_compact_unevictable_allowed __read_mostly = 1; > + > +/* > * Isolate all pages that can be migrated from the first suitable block, > * starting at the block pointed to by the migrate scanner pfn within > * compact_control. > @@ -1057,6 +1063,7 @@ static isolate_migrate_t isolate_migratepages(struct > zone *zone, > unsigned long low_pfn, end_pfn; > struct page *page; > const isolate_mode_t isolate_mode = > + (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) | > (cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0); > > /* > -- > 1.7.9.5 > -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
