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 <emunson@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
> 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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