Hi Mel,
Just one questoin below.
On Wed, Aug 08, 2012 at 08:08:42PM +0100, Mel Gorman wrote:
> While compaction is migrating pages to free up large contiguous blocks for
> allocation it races with other allocation requests that may steal these
> blocks or break them up. This patch alters direct compaction to capture a
> suitable free page as soon as it becomes available to reduce this race. It
> uses similar logic to split_free_page() to ensure that watermarks are
> still obeyed.
>
> Signed-off-by: Mel Gorman <mgor...@suse.de>
> Reviewed-by: Rik van Riel <r...@redhat.com>
> ---
> include/linux/compaction.h | 4 +--
> include/linux/mm.h | 1 +
> mm/compaction.c | 71
> +++++++++++++++++++++++++++++++++++++-------
> mm/internal.h | 1 +
> mm/page_alloc.c | 63 +++++++++++++++++++++++++++++----------
> 5 files changed, 111 insertions(+), 29 deletions(-)
>
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index 51a90b7..5673459 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -22,7 +22,7 @@ extern int sysctl_extfrag_handler(struct ctl_table *table,
> int write,
> extern int fragmentation_index(struct zone *zone, unsigned int order);
> extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
> int order, gfp_t gfp_mask, nodemask_t *mask,
> - bool sync);
> + bool sync, struct page **page);
> extern int compact_pgdat(pg_data_t *pgdat, int order);
> extern unsigned long compaction_suitable(struct zone *zone, int order);
>
> @@ -64,7 +64,7 @@ static inline bool compaction_deferred(struct zone *zone,
> int order)
> #else
> static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
> int order, gfp_t gfp_mask, nodemask_t *nodemask,
> - bool sync)
> + bool sync, struct page **page)
> {
> return COMPACT_CONTINUE;
> }
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index b36d08c..0812e86 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -454,6 +454,7 @@ void put_pages_list(struct list_head *pages);
>
> void split_page(struct page *page, unsigned int order);
> int split_free_page(struct page *page);
> +int capture_free_page(struct page *page, int alloc_order, int migratetype);
>
> /*
> * Compound pages have a destructor function. Provide a
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 95ca967..63af8d2 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -50,6 +50,41 @@ static inline bool migrate_async_suitable(int migratetype)
> return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
> }
>
> +static void compact_capture_page(struct compact_control *cc)
> +{
> + unsigned long flags;
> + int mtype;
> +
> + if (!cc->page || *cc->page)
> + return;
> +
> + /* Speculatively examine the free lists without zone lock */
> + for (mtype = 0; mtype < MIGRATE_PCPTYPES; mtype++) {
> + int order;
> + for (order = cc->order; order < MAX_ORDER; order++) {
> + struct page *page;
> + struct free_area *area;
> + area = &(cc->zone->free_area[order]);
> + if (list_empty(&area->free_list[mtype]))
> + continue;
> +
> + /* Take the lock and attempt capture of the page */
> + spin_lock_irqsave(&cc->zone->lock, flags);
> + if (!list_empty(&area->free_list[mtype])) {
> + page = list_entry(area->free_list[mtype].next,
> + struct page, lru);
> + if (capture_free_page(page, cc->order, mtype)) {
> + spin_unlock_irqrestore(&cc->zone->lock,
> + flags);
> + *cc->page = page;
> + return;
> + }
> + }
> + spin_unlock_irqrestore(&cc->zone->lock, flags);
> + }
> + }
> +}
> +
> /*
> * Isolate free pages onto a private freelist. Caller must hold zone->lock.
> * If @strict is true, will abort returning 0 on any invalid PFNs or non-free
> @@ -561,7 +596,6 @@ static isolate_migrate_t isolate_migratepages(struct zone
> *zone,
> static int compact_finished(struct zone *zone,
> struct compact_control *cc)
> {
> - unsigned int order;
> unsigned long watermark;
>
> if (fatal_signal_pending(current))
> @@ -586,14 +620,22 @@ static int compact_finished(struct zone *zone,
> return COMPACT_CONTINUE;
>
> /* Direct compactor: Is a suitable page free? */
> - for (order = cc->order; order < MAX_ORDER; order++) {
> - /* Job done if page is free of the right migratetype */
> - if
> (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
> - return COMPACT_PARTIAL;
> -
> - /* Job done if allocation would set block type */
> - if (order >= pageblock_order && zone->free_area[order].nr_free)
> + if (cc->page) {
> + /* Was a suitable page captured? */
> + if (*cc->page)
> return COMPACT_PARTIAL;
> + } else {
> + unsigned int order;
> + for (order = cc->order; order < MAX_ORDER; order++) {
> + struct free_area *area = &zone->free_area[cc->order];
> + /* Job done if page is free of the right migratetype */
> + if (!list_empty(&area->free_list[cc->migratetype]))
> + return COMPACT_PARTIAL;
> +
> + /* Job done if allocation would set block type */
> + if (cc->order >= pageblock_order && area->nr_free)
> + return COMPACT_PARTIAL;
> + }
> }
>
> return COMPACT_CONTINUE;
> @@ -708,6 +750,10 @@ static int compact_zone(struct zone *zone, struct
> compact_control *cc)
> goto out;
> }
> }
> +
> + /* Capture a page now if it is a suitable size */
Why do we capture only when we migrate MIGRATE_MOVABLE type?
If you have a reasone, it should have been added as comment.
> + if (cc->migratetype == MIGRATE_MOVABLE)
> + compact_capture_page(cc);
> }
>
> out:
> @@ -720,7 +766,7 @@ out:
>
> static unsigned long compact_zone_order(struct zone *zone,
> int order, gfp_t gfp_mask,
> - bool sync)
> + bool sync, struct page **page)
> {
> struct compact_control cc = {
> .nr_freepages = 0,
> @@ -729,6 +775,7 @@ static unsigned long compact_zone_order(struct zone *zone,
> .migratetype = allocflags_to_migratetype(gfp_mask),
> .zone = zone,
> .sync = sync,
> + .page = page,
> };
> INIT_LIST_HEAD(&cc.freepages);
> INIT_LIST_HEAD(&cc.migratepages);
> @@ -750,7 +797,7 @@ int sysctl_extfrag_threshold = 500;
> */
> unsigned long try_to_compact_pages(struct zonelist *zonelist,
> int order, gfp_t gfp_mask, nodemask_t *nodemask,
> - bool sync)
> + bool sync, struct page **page)
> {
> enum zone_type high_zoneidx = gfp_zone(gfp_mask);
> int may_enter_fs = gfp_mask & __GFP_FS;
> @@ -770,7 +817,7 @@ unsigned long try_to_compact_pages(struct zonelist
> *zonelist,
> nodemask) {
> int status;
>
> - status = compact_zone_order(zone, order, gfp_mask, sync);
> + status = compact_zone_order(zone, order, gfp_mask, sync, page);
> rc = max(status, rc);
>
> /* If a normal allocation would succeed, stop compacting */
> @@ -825,6 +872,7 @@ int compact_pgdat(pg_data_t *pgdat, int order)
> struct compact_control cc = {
> .order = order,
> .sync = false,
> + .page = NULL,
> };
>
> return __compact_pgdat(pgdat, &cc);
> @@ -835,6 +883,7 @@ static int compact_node(int nid)
> struct compact_control cc = {
> .order = -1,
> .sync = true,
> + .page = NULL,
> };
>
> return __compact_pgdat(NODE_DATA(nid), &cc);
> diff --git a/mm/internal.h b/mm/internal.h
> index 2ba87fb..9156714 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -124,6 +124,7 @@ struct compact_control {
> int order; /* order a direct compactor needs */
> int migratetype; /* MOVABLE, RECLAIMABLE etc */
> struct zone *zone;
> + struct page **page; /* Page captured of requested size */
> };
>
> unsigned long
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4a4f921..adc3aa8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1374,16 +1374,11 @@ void split_page(struct page *page, unsigned int order)
> }
>
> /*
> - * Similar to split_page except the page is already free. As this is only
> - * being used for migration, the migratetype of the block also changes.
> - * As this is called with interrupts disabled, the caller is responsible
> - * for calling arch_alloc_page() and kernel_map_page() after interrupts
> - * are enabled.
> - *
> - * Note: this is probably too low level an operation for use in drivers.
> - * Please consult with lkml before using this in your driver.
> + * Similar to the split_page family of functions except that the page
> + * required at the given order and being isolated now to prevent races
> + * with parallel allocators
> */
> -int split_free_page(struct page *page)
> +int capture_free_page(struct page *page, int alloc_order, int migratetype)
> {
> unsigned int order;
> unsigned long watermark;
> @@ -1405,10 +1400,11 @@ int split_free_page(struct page *page)
> rmv_page_order(page);
> __mod_zone_page_state(zone, NR_FREE_PAGES, -(1UL << order));
>
> - /* Split into individual pages */
> - set_page_refcounted(page);
> - split_page(page, order);
> + if (alloc_order != order)
> + expand(zone, page, alloc_order, order,
> + &zone->free_area[order], migratetype);
>
> + /* Set the pageblock if the captured page is at least a pageblock */
> if (order >= pageblock_order - 1) {
> struct page *endpage = page + (1 << order) - 1;
> for (; page < endpage; page += pageblock_nr_pages) {
> @@ -1419,7 +1415,35 @@ int split_free_page(struct page *page)
> }
> }
>
> - return 1 << order;
> + return 1UL << order;
> +}
> +
> +/*
> + * Similar to split_page except the page is already free. As this is only
> + * being used for migration, the migratetype of the block also changes.
> + * As this is called with interrupts disabled, the caller is responsible
> + * for calling arch_alloc_page() and kernel_map_page() after interrupts
> + * are enabled.
> + *
> + * Note: this is probably too low level an operation for use in drivers.
> + * Please consult with lkml before using this in your driver.
> + */
> +int split_free_page(struct page *page)
> +{
> + unsigned int order;
> + int nr_pages;
> +
> + BUG_ON(!PageBuddy(page));
> + order = page_order(page);
> +
> + nr_pages = capture_free_page(page, order, 0);
> + if (!nr_pages)
> + return 0;
> +
> + /* Split into individual pages */
> + set_page_refcounted(page);
> + split_page(page, order);
> + return nr_pages;
> }
>
> /*
> @@ -2065,7 +2089,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned
> int order,
> bool *deferred_compaction,
> unsigned long *did_some_progress)
> {
> - struct page *page;
> + struct page *page = NULL;
>
> if (!order)
> return NULL;
> @@ -2077,10 +2101,16 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned
> int order,
>
> current->flags |= PF_MEMALLOC;
> *did_some_progress = try_to_compact_pages(zonelist, order, gfp_mask,
> - nodemask, sync_migration);
> + nodemask, sync_migration, &page);
> current->flags &= ~PF_MEMALLOC;
> - if (*did_some_progress != COMPACT_SKIPPED) {
>
> + /* If compaction captured a page, prep and use it */
> + if (page) {
> + prep_new_page(page, order, gfp_mask);
> + goto got_page;
> + }
> +
> + if (*did_some_progress != COMPACT_SKIPPED) {
> /* Page migration frees to the PCP lists but we want merging */
> drain_pages(get_cpu());
> put_cpu();
> @@ -2090,6 +2120,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned
> int order,
> alloc_flags, preferred_zone,
> migratetype);
> if (page) {
> +got_page:
> preferred_zone->compact_considered = 0;
> preferred_zone->compact_defer_shift = 0;
> if (order >= preferred_zone->compact_order_failed)
> --
> 1.7.9.2
>
> --
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--
Kind regards,
Minchan Kim
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