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    SubjectRe: [ 06/73] mm: compaction: introduce sync-light migration for use by compaction
    On Tue, Jul 31, 2012 at 05:43:16AM +0100, Ben Hutchings wrote:
    > 3.2-stable review patch. If anyone has any objections, please let me know.
    >
    > ------------------
    >
    > From: Mel Gorman <mgorman@suse.de>
    >
    > commit a6bc32b899223a877f595ef9ddc1e89ead5072b8 upstream.

    We need also to pick recent fix dc32f63453f56d07a1073a697dcd843dd3098c09 after
    applying this one.

    >
    > Stable note: Not tracked in Buzilla. This was part of a series that
    > reduced interactivity stalls experienced when THP was enabled.
    > These stalls were particularly noticable when copying data
    > to a USB stick but the experiences for users varied a lot.
    >
    > This patch adds a lightweight sync migrate operation MIGRATE_SYNC_LIGHT
    > mode that avoids writing back pages to backing storage. Async compaction
    > maps to MIGRATE_ASYNC while sync compaction maps to MIGRATE_SYNC_LIGHT.
    > For other migrate_pages users such as memory hotplug, MIGRATE_SYNC is
    > used.
    >
    > This avoids sync compaction stalling for an excessive length of time,
    > particularly when copying files to a USB stick where there might be a
    > large number of dirty pages backed by a filesystem that does not support
    > ->writepages.
    >
    > [aarcange@redhat.com: This patch is heavily based on Andrea's work]
    > [akpm@linux-foundation.org: fix fs/nfs/write.c build]
    > [akpm@linux-foundation.org: fix fs/btrfs/disk-io.c build]
    > Signed-off-by: Mel Gorman <mgorman@suse.de>
    > Reviewed-by: Rik van Riel <riel@redhat.com>
    > Cc: Andrea Arcangeli <aarcange@redhat.com>
    > Cc: Minchan Kim <minchan.kim@gmail.com>
    > Cc: Dave Jones <davej@redhat.com>
    > Cc: Jan Kara <jack@suse.cz>
    > Cc: Andy Isaacson <adi@hexapodia.org>
    > Cc: Nai Xia <nai.xia@gmail.com>
    > Cc: Johannes Weiner <jweiner@redhat.com>
    > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    > Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    > ---
    > fs/btrfs/disk-io.c | 5 +--
    > fs/hugetlbfs/inode.c | 2 +-
    > fs/nfs/internal.h | 2 +-
    > fs/nfs/write.c | 4 +--
    > include/linux/fs.h | 6 ++--
    > include/linux/migrate.h | 23 +++++++++++---
    > mm/compaction.c | 2 +-
    > mm/memory-failure.c | 2 +-
    > mm/memory_hotplug.c | 2 +-
    > mm/mempolicy.c | 2 +-
    > mm/migrate.c | 78 ++++++++++++++++++++++++++---------------------
    > 11 files changed, 76 insertions(+), 52 deletions(-)
    >
    > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
    > index 1375494..d852566 100644
    > --- a/fs/btrfs/disk-io.c
    > +++ b/fs/btrfs/disk-io.c
    > @@ -872,7 +872,8 @@ static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
    >
    > #ifdef CONFIG_MIGRATION
    > static int btree_migratepage(struct address_space *mapping,
    > - struct page *newpage, struct page *page, bool sync)
    > + struct page *newpage, struct page *page,
    > + enum migrate_mode mode)
    > {
    > /*
    > * we can't safely write a btree page from here,
    > @@ -887,7 +888,7 @@ static int btree_migratepage(struct address_space *mapping,
    > if (page_has_private(page) &&
    > !try_to_release_page(page, GFP_KERNEL))
    > return -EAGAIN;
    > - return migrate_page(mapping, newpage, page, sync);
    > + return migrate_page(mapping, newpage, page, mode);
    > }
    > #endif
    >
    > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
    > index 06fd460..1e85a7a 100644
    > --- a/fs/hugetlbfs/inode.c
    > +++ b/fs/hugetlbfs/inode.c
    > @@ -584,7 +584,7 @@ static int hugetlbfs_set_page_dirty(struct page *page)
    >
    > static int hugetlbfs_migrate_page(struct address_space *mapping,
    > struct page *newpage, struct page *page,
    > - bool sync)
    > + enum migrate_mode mode)
    > {
    > int rc;
    >
    > diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
    > index 114398a..8102db9 100644
    > --- a/fs/nfs/internal.h
    > +++ b/fs/nfs/internal.h
    > @@ -332,7 +332,7 @@ void nfs_commit_release_pages(struct nfs_write_data *data);
    >
    > #ifdef CONFIG_MIGRATION
    > extern int nfs_migrate_page(struct address_space *,
    > - struct page *, struct page *, bool);
    > + struct page *, struct page *, enum migrate_mode);
    > #else
    > #define nfs_migrate_page NULL
    > #endif
    > diff --git a/fs/nfs/write.c b/fs/nfs/write.c
    > index 889e98b..834f0fe 100644
    > --- a/fs/nfs/write.c
    > +++ b/fs/nfs/write.c
    > @@ -1688,7 +1688,7 @@ out_error:
    >
    > #ifdef CONFIG_MIGRATION
    > int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
    > - struct page *page, bool sync)
    > + struct page *page, enum migrate_mode mode)
    > {
    > /*
    > * If PagePrivate is set, then the page is currently associated with
    > @@ -1703,7 +1703,7 @@ int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
    >
    > nfs_fscache_release_page(page, GFP_KERNEL);
    >
    > - return migrate_page(mapping, newpage, page, sync);
    > + return migrate_page(mapping, newpage, page, mode);
    > }
    > #endif
    >
    > diff --git a/include/linux/fs.h b/include/linux/fs.h
    > index b92b73d..e694bd4 100644
    > --- a/include/linux/fs.h
    > +++ b/include/linux/fs.h
    > @@ -525,6 +525,7 @@ enum positive_aop_returns {
    > struct page;
    > struct address_space;
    > struct writeback_control;
    > +enum migrate_mode;
    >
    > struct iov_iter {
    > const struct iovec *iov;
    > @@ -614,7 +615,7 @@ struct address_space_operations {
    > * is false, it must not block.
    > */
    > int (*migratepage) (struct address_space *,
    > - struct page *, struct page *, bool);
    > + struct page *, struct page *, enum migrate_mode);
    > int (*launder_page) (struct page *);
    > int (*is_partially_uptodate) (struct page *, read_descriptor_t *,
    > unsigned long);
    > @@ -2540,7 +2541,8 @@ extern int generic_check_addressable(unsigned, u64);
    >
    > #ifdef CONFIG_MIGRATION
    > extern int buffer_migrate_page(struct address_space *,
    > - struct page *, struct page *, bool);
    > + struct page *, struct page *,
    > + enum migrate_mode);
    > #else
    > #define buffer_migrate_page NULL
    > #endif
    > diff --git a/include/linux/migrate.h b/include/linux/migrate.h
    > index 14e6d2a..eaf8674 100644
    > --- a/include/linux/migrate.h
    > +++ b/include/linux/migrate.h
    > @@ -6,18 +6,31 @@
    >
    > typedef struct page *new_page_t(struct page *, unsigned long private, int **);
    >
    > +/*
    > + * MIGRATE_ASYNC means never block
    > + * MIGRATE_SYNC_LIGHT in the current implementation means to allow blocking
    > + * on most operations but not ->writepage as the potential stall time
    > + * is too significant
    > + * MIGRATE_SYNC will block when migrating pages
    > + */
    > +enum migrate_mode {
    > + MIGRATE_ASYNC,
    > + MIGRATE_SYNC_LIGHT,
    > + MIGRATE_SYNC,
    > +};
    > +
    > #ifdef CONFIG_MIGRATION
    > #define PAGE_MIGRATION 1
    >
    > extern void putback_lru_pages(struct list_head *l);
    > extern int migrate_page(struct address_space *,
    > - struct page *, struct page *, bool);
    > + struct page *, struct page *, enum migrate_mode);
    > extern int migrate_pages(struct list_head *l, new_page_t x,
    > unsigned long private, bool offlining,
    > - bool sync);
    > + enum migrate_mode mode);
    > extern int migrate_huge_pages(struct list_head *l, new_page_t x,
    > unsigned long private, bool offlining,
    > - bool sync);
    > + enum migrate_mode mode);
    >
    > extern int fail_migrate_page(struct address_space *,
    > struct page *, struct page *);
    > @@ -36,10 +49,10 @@ extern int migrate_huge_page_move_mapping(struct address_space *mapping,
    > static inline void putback_lru_pages(struct list_head *l) {}
    > static inline int migrate_pages(struct list_head *l, new_page_t x,
    > unsigned long private, bool offlining,
    > - bool sync) { return -ENOSYS; }
    > + enum migrate_mode mode) { return -ENOSYS; }
    > static inline int migrate_huge_pages(struct list_head *l, new_page_t x,
    > unsigned long private, bool offlining,
    > - bool sync) { return -ENOSYS; }
    > + enum migrate_mode mode) { return -ENOSYS; }
    >
    > static inline int migrate_prep(void) { return -ENOSYS; }
    > static inline int migrate_prep_local(void) { return -ENOSYS; }
    > diff --git a/mm/compaction.c b/mm/compaction.c
    > index fb29158..71a58f6 100644
    > --- a/mm/compaction.c
    > +++ b/mm/compaction.c
    > @@ -557,7 +557,7 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
    > nr_migrate = cc->nr_migratepages;
    > err = migrate_pages(&cc->migratepages, compaction_alloc,
    > (unsigned long)cc, false,
    > - cc->sync);
    > + cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC);
    > update_nr_listpages(cc);
    > nr_remaining = cc->nr_migratepages;
    >
    > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
    > index 06d3479..56080ea 100644
    > --- a/mm/memory-failure.c
    > +++ b/mm/memory-failure.c
    > @@ -1557,7 +1557,7 @@ int soft_offline_page(struct page *page, int flags)
    > page_is_file_cache(page));
    > list_add(&page->lru, &pagelist);
    > ret = migrate_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL,
    > - 0, true);
    > + 0, MIGRATE_SYNC);
    > if (ret) {
    > putback_lru_pages(&pagelist);
    > pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
    > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
    > index 2168489..6629faf 100644
    > --- a/mm/memory_hotplug.c
    > +++ b/mm/memory_hotplug.c
    > @@ -809,7 +809,7 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
    > }
    > /* this function returns # of failed pages */
    > ret = migrate_pages(&source, hotremove_migrate_alloc, 0,
    > - true, true);
    > + true, MIGRATE_SYNC);
    > if (ret)
    > putback_lru_pages(&source);
    > }
    > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
    > index e3d58f0..06b145f 100644
    > --- a/mm/mempolicy.c
    > +++ b/mm/mempolicy.c
    > @@ -942,7 +942,7 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
    >
    > if (!list_empty(&pagelist)) {
    > err = migrate_pages(&pagelist, new_node_page, dest,
    > - false, true);
    > + false, MIGRATE_SYNC);
    > if (err)
    > putback_lru_pages(&pagelist);
    > }
    > diff --git a/mm/migrate.c b/mm/migrate.c
    > index 4e86f3b..9871a56 100644
    > --- a/mm/migrate.c
    > +++ b/mm/migrate.c
    > @@ -218,12 +218,13 @@ out:
    >
    > #ifdef CONFIG_BLOCK
    > /* Returns true if all buffers are successfully locked */
    > -static bool buffer_migrate_lock_buffers(struct buffer_head *head, bool sync)
    > +static bool buffer_migrate_lock_buffers(struct buffer_head *head,
    > + enum migrate_mode mode)
    > {
    > struct buffer_head *bh = head;
    >
    > /* Simple case, sync compaction */
    > - if (sync) {
    > + if (mode != MIGRATE_ASYNC) {
    > do {
    > get_bh(bh);
    > lock_buffer(bh);
    > @@ -259,7 +260,7 @@ static bool buffer_migrate_lock_buffers(struct buffer_head *head, bool sync)
    > }
    > #else
    > static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
    > - bool sync)
    > + enum migrate_mode mode)
    > {
    > return true;
    > }
    > @@ -275,7 +276,7 @@ static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
    > */
    > static int migrate_page_move_mapping(struct address_space *mapping,
    > struct page *newpage, struct page *page,
    > - struct buffer_head *head, bool sync)
    > + struct buffer_head *head, enum migrate_mode mode)
    > {
    > int expected_count;
    > void **pslot;
    > @@ -311,7 +312,8 @@ static int migrate_page_move_mapping(struct address_space *mapping,
    > * the mapping back due to an elevated page count, we would have to
    > * block waiting on other references to be dropped.
    > */
    > - if (!sync && head && !buffer_migrate_lock_buffers(head, sync)) {
    > + if (mode == MIGRATE_ASYNC && head &&
    > + !buffer_migrate_lock_buffers(head, mode)) {
    > page_unfreeze_refs(page, expected_count);
    > spin_unlock_irq(&mapping->tree_lock);
    > return -EAGAIN;
    > @@ -472,13 +474,14 @@ EXPORT_SYMBOL(fail_migrate_page);
    > * Pages are locked upon entry and exit.
    > */
    > int migrate_page(struct address_space *mapping,
    > - struct page *newpage, struct page *page, bool sync)
    > + struct page *newpage, struct page *page,
    > + enum migrate_mode mode)
    > {
    > int rc;
    >
    > BUG_ON(PageWriteback(page)); /* Writeback must be complete */
    >
    > - rc = migrate_page_move_mapping(mapping, newpage, page, NULL, sync);
    > + rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode);
    >
    > if (rc)
    > return rc;
    > @@ -495,17 +498,17 @@ EXPORT_SYMBOL(migrate_page);
    > * exist.
    > */
    > int buffer_migrate_page(struct address_space *mapping,
    > - struct page *newpage, struct page *page, bool sync)
    > + struct page *newpage, struct page *page, enum migrate_mode mode)
    > {
    > struct buffer_head *bh, *head;
    > int rc;
    >
    > if (!page_has_buffers(page))
    > - return migrate_page(mapping, newpage, page, sync);
    > + return migrate_page(mapping, newpage, page, mode);
    >
    > head = page_buffers(page);
    >
    > - rc = migrate_page_move_mapping(mapping, newpage, page, head, sync);
    > + rc = migrate_page_move_mapping(mapping, newpage, page, head, mode);
    >
    > if (rc)
    > return rc;
    > @@ -515,8 +518,8 @@ int buffer_migrate_page(struct address_space *mapping,
    > * with an IRQ-safe spinlock held. In the sync case, the buffers
    > * need to be locked now
    > */
    > - if (sync)
    > - BUG_ON(!buffer_migrate_lock_buffers(head, sync));
    > + if (mode != MIGRATE_ASYNC)
    > + BUG_ON(!buffer_migrate_lock_buffers(head, mode));
    >
    > ClearPagePrivate(page);
    > set_page_private(newpage, page_private(page));
    > @@ -593,10 +596,11 @@ static int writeout(struct address_space *mapping, struct page *page)
    > * Default handling if a filesystem does not provide a migration function.
    > */
    > static int fallback_migrate_page(struct address_space *mapping,
    > - struct page *newpage, struct page *page, bool sync)
    > + struct page *newpage, struct page *page, enum migrate_mode mode)
    > {
    > if (PageDirty(page)) {
    > - if (!sync)
    > + /* Only writeback pages in full synchronous migration */
    > + if (mode != MIGRATE_SYNC)
    > return -EBUSY;
    > return writeout(mapping, page);
    > }
    > @@ -609,7 +613,7 @@ static int fallback_migrate_page(struct address_space *mapping,
    > !try_to_release_page(page, GFP_KERNEL))
    > return -EAGAIN;
    >
    > - return migrate_page(mapping, newpage, page, sync);
    > + return migrate_page(mapping, newpage, page, mode);
    > }
    >
    > /*
    > @@ -624,7 +628,7 @@ static int fallback_migrate_page(struct address_space *mapping,
    > * == 0 - success
    > */
    > static int move_to_new_page(struct page *newpage, struct page *page,
    > - int remap_swapcache, bool sync)
    > + int remap_swapcache, enum migrate_mode mode)
    > {
    > struct address_space *mapping;
    > int rc;
    > @@ -645,7 +649,7 @@ static int move_to_new_page(struct page *newpage, struct page *page,
    >
    > mapping = page_mapping(page);
    > if (!mapping)
    > - rc = migrate_page(mapping, newpage, page, sync);
    > + rc = migrate_page(mapping, newpage, page, mode);
    > else if (mapping->a_ops->migratepage)
    > /*
    > * Most pages have a mapping and most filesystems provide a
    > @@ -654,9 +658,9 @@ static int move_to_new_page(struct page *newpage, struct page *page,
    > * is the most common path for page migration.
    > */
    > rc = mapping->a_ops->migratepage(mapping,
    > - newpage, page, sync);
    > + newpage, page, mode);
    > else
    > - rc = fallback_migrate_page(mapping, newpage, page, sync);
    > + rc = fallback_migrate_page(mapping, newpage, page, mode);
    >
    > if (rc) {
    > newpage->mapping = NULL;
    > @@ -671,7 +675,7 @@ static int move_to_new_page(struct page *newpage, struct page *page,
    > }
    >
    > static int __unmap_and_move(struct page *page, struct page *newpage,
    > - int force, bool offlining, bool sync)
    > + int force, bool offlining, enum migrate_mode mode)
    > {
    > int rc = -EAGAIN;
    > int remap_swapcache = 1;
    > @@ -680,7 +684,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
    > struct anon_vma *anon_vma = NULL;
    >
    > if (!trylock_page(page)) {
    > - if (!force || !sync)
    > + if (!force || mode == MIGRATE_ASYNC)
    > goto out;
    >
    > /*
    > @@ -726,10 +730,12 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
    >
    > if (PageWriteback(page)) {
    > /*
    > - * For !sync, there is no point retrying as the retry loop
    > - * is expected to be too short for PageWriteback to be cleared
    > + * Only in the case of a full syncronous migration is it
    > + * necessary to wait for PageWriteback. In the async case,
    > + * the retry loop is too short and in the sync-light case,
    > + * the overhead of stalling is too much
    > */
    > - if (!sync) {
    > + if (mode != MIGRATE_SYNC) {
    > rc = -EBUSY;
    > goto uncharge;
    > }
    > @@ -800,7 +806,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
    >
    > skip_unmap:
    > if (!page_mapped(page))
    > - rc = move_to_new_page(newpage, page, remap_swapcache, sync);
    > + rc = move_to_new_page(newpage, page, remap_swapcache, mode);
    >
    > if (rc && remap_swapcache)
    > remove_migration_ptes(page, page);
    > @@ -823,7 +829,8 @@ out:
    > * to the newly allocated page in newpage.
    > */
    > static int unmap_and_move(new_page_t get_new_page, unsigned long private,
    > - struct page *page, int force, bool offlining, bool sync)
    > + struct page *page, int force, bool offlining,
    > + enum migrate_mode mode)
    > {
    > int rc = 0;
    > int *result = NULL;
    > @@ -843,7 +850,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
    > if (unlikely(split_huge_page(page)))
    > goto out;
    >
    > - rc = __unmap_and_move(page, newpage, force, offlining, sync);
    > + rc = __unmap_and_move(page, newpage, force, offlining, mode);
    > out:
    > if (rc != -EAGAIN) {
    > /*
    > @@ -891,7 +898,8 @@ out:
    > */
    > static int unmap_and_move_huge_page(new_page_t get_new_page,
    > unsigned long private, struct page *hpage,
    > - int force, bool offlining, bool sync)
    > + int force, bool offlining,
    > + enum migrate_mode mode)
    > {
    > int rc = 0;
    > int *result = NULL;
    > @@ -904,7 +912,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
    > rc = -EAGAIN;
    >
    > if (!trylock_page(hpage)) {
    > - if (!force || !sync)
    > + if (!force || mode != MIGRATE_SYNC)
    > goto out;
    > lock_page(hpage);
    > }
    > @@ -915,7 +923,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
    > try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
    >
    > if (!page_mapped(hpage))
    > - rc = move_to_new_page(new_hpage, hpage, 1, sync);
    > + rc = move_to_new_page(new_hpage, hpage, 1, mode);
    >
    > if (rc)
    > remove_migration_ptes(hpage, hpage);
    > @@ -958,7 +966,7 @@ out:
    > */
    > int migrate_pages(struct list_head *from,
    > new_page_t get_new_page, unsigned long private, bool offlining,
    > - bool sync)
    > + enum migrate_mode mode)
    > {
    > int retry = 1;
    > int nr_failed = 0;
    > @@ -979,7 +987,7 @@ int migrate_pages(struct list_head *from,
    >
    > rc = unmap_and_move(get_new_page, private,
    > page, pass > 2, offlining,
    > - sync);
    > + mode);
    >
    > switch(rc) {
    > case -ENOMEM:
    > @@ -1009,7 +1017,7 @@ out:
    >
    > int migrate_huge_pages(struct list_head *from,
    > new_page_t get_new_page, unsigned long private, bool offlining,
    > - bool sync)
    > + enum migrate_mode mode)
    > {
    > int retry = 1;
    > int nr_failed = 0;
    > @@ -1026,7 +1034,7 @@ int migrate_huge_pages(struct list_head *from,
    >
    > rc = unmap_and_move_huge_page(get_new_page,
    > private, page, pass > 2, offlining,
    > - sync);
    > + mode);
    >
    > switch(rc) {
    > case -ENOMEM:
    > @@ -1155,7 +1163,7 @@ set_status:
    > err = 0;
    > if (!list_empty(&pagelist)) {
    > err = migrate_pages(&pagelist, new_page_node,
    > - (unsigned long)pm, 0, true);
    > + (unsigned long)pm, 0, MIGRATE_SYNC);
    > if (err)
    > putback_lru_pages(&pagelist);
    > }
    >
    >
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