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SubjectRe: [f2fs-dev] [PATCH] f2fs: avoid migratepage for atomic written page
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Hi Jaegeuk,

On 2017/7/4 7:08, Jaegeuk Kim wrote:
> In order to avoid lock contention for atomic written pages, we'd better give
> EAGAIN in f2fs_migrate_page. We expect it will be released soon as transaction
> commits.

Hmm.. if atomic write is triggered intensively, there is little change to
migrate fragmented page.

How about detecting migrate mode here, for MIGRATE_SYNC case, let it moving
the page; for MIGRATE_ASYNC/MIGRATE_SYNC_LIGHT case, the migration priority
is lower, we can return EAGAIN.

Thanks,

>
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
> fs/f2fs/data.c | 35 ++++++++++-------------------------
> 1 file changed, 10 insertions(+), 25 deletions(-)
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index d58b81213a86..1458e3a6d630 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2197,41 +2197,26 @@ static sector_t f2fs_bmap(struct address_space *mapping, sector_t block)
> int f2fs_migrate_page(struct address_space *mapping,
> struct page *newpage, struct page *page, enum migrate_mode mode)
> {
> - int rc, extra_count;
> - struct f2fs_inode_info *fi = F2FS_I(mapping->host);
> - bool atomic_written = IS_ATOMIC_WRITTEN_PAGE(page);
> + int rc;
>
> - BUG_ON(PageWriteback(page));
> -
> - /* migrating an atomic written page is safe with the inmem_lock hold */
> - if (atomic_written && !mutex_trylock(&fi->inmem_lock))
> + /*
> + * We'd better return EAGAIN for atomic pages, which will be committed
> + * sooner or later. Don't botter transactions with inmem_lock.
> + */
> + if (IS_ATOMIC_WRITTEN_PAGE(page))
> return -EAGAIN;
>
> + BUG_ON(PageWriteback(page)); /* Writeback must be complete */
> +
> /*
> * A reference is expected if PagePrivate set when move mapping,
> * however F2FS breaks this for maintaining dirty page counts when
> * truncating pages. So here adjusting the 'extra_count' make it work.
> */
> - extra_count = (atomic_written ? 1 : 0) - page_has_private(page);
> rc = migrate_page_move_mapping(mapping, newpage,
> - page, NULL, mode, extra_count);
> - if (rc != MIGRATEPAGE_SUCCESS) {
> - if (atomic_written)
> - mutex_unlock(&fi->inmem_lock);
> + page, NULL, mode, (page_has_private(page) ? -1 : 0));
> + if (rc != MIGRATEPAGE_SUCCESS)
> return rc;
> - }
> -
> - if (atomic_written) {
> - struct inmem_pages *cur;
> - list_for_each_entry(cur, &fi->inmem_pages, list)
> - if (cur->page == page) {
> - cur->page = newpage;
> - break;
> - }
> - mutex_unlock(&fi->inmem_lock);
> - put_page(page);
> - get_page(newpage);
> - }
>
> if (PagePrivate(page))
> SetPagePrivate(newpage);
>

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