On Thu, 12 Mar 2015, Eric B Munson wrote: > Currently, pages which are marked as unevictable are protected from > compaction, but not from other types of migration. The mlock > desctription does not promise that all page faults will be avoided, only > major ones so this protection is not necessary. This extra protection > can cause problems for applications that are using mlock to avoid > swapping pages out, but require order > 0 allocations to continue to > succeed in a fragmented environment. This patch adds a sysctl entry > that will be used to allow root to enable compaction of unevictable > pages. > > 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: [email protected] > Cc: [email protected] > --- > Changes from V3: > Instead of removing the ISOLATE_UNEVICTABLE mode and checks, allow the > sysadmin to control if compaction of unevictable pages is allowable. > > include/linux/compaction.h | 1 + > kernel/sysctl.c | 7 +++++++ > mm/compaction.c | 3 +++ > 3 files changed, 11 insertions(+) > > diff --git a/include/linux/compaction.h b/include/linux/compaction.h > index a014559..9dd7e7c 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; > > 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..cc1a678 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -1313,6 +1313,13 @@ static struct ctl_table vm_table[] = { > .extra1 = &min_extfrag_threshold, > .extra2 = &max_extfrag_threshold, > }, > + { > + .procname = "compact_unevictable", > + .data = &sysctl_compact_unevictable, > + .maxlen = sizeof(int), > + .mode = 0644, > + .proc_handler = proc_dointvec, > + }, > > #endif /* CONFIG_COMPACTION */ > { > diff --git a/mm/compaction.c b/mm/compaction.c > index 8c0d945..b2c1e4e 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1046,6 +1046,8 @@ typedef enum { > ISOLATE_SUCCESS, /* Pages isolated, migrate */ > } isolate_migrate_t; > > +int sysctl_compact_unevictable; > + > /* > * Isolate all pages that can be migrated from the first suitable block, > * starting at the block pointed to by the migrate scanner pfn within > @@ -1057,6 +1059,7 @@ 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 ? ISOLATE_UNEVICTABLE: 0) |
Sorry, missed the space following the :, if this idea is acceptable, I will send a patch with the correct whitespace. > (cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0); > > /* > -- > 1.7.9.5 >
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