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Message-ID: <CAPhsuW7Hu6jBn-ti7S2cJhO1YQYg_RDZUgkqtgFO8zpBMV_9LA@mail.gmail.com>
Date: Fri, 1 Mar 2019 11:12:44 -0800
From: Song Liu <liu.song.a23@...il.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: "Kirill A. Shutemov" <kirill@...temov.name>, linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org,
open list <linux-kernel@...r.kernel.org>,
Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
William Kucharski <william.kucharski@...cle.com>
Subject: Re: [PATCH v3] page cache: Store only head pages in i_pages
On Fri, Feb 15, 2019 at 2:25 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> Transparent Huge Pages are currently stored in i_pages as pointers to
> consecutive subpages. This patch changes that to storing consecutive
> pointers to the head page in preparation for storing huge pages more
> efficiently in i_pages.
>
> Large parts of this are "inspired" by Kirill's patch
> https://lore.kernel.org/lkml/20170126115819.58875-2-kirill.shutemov@linux.intel.com/
>
> Signed-off-by: Matthew Wilcox <willy@...radead.org>
> Acked-by: Jan Kara <jack@...e.cz>
> Reviewed-by: Kirill Shutemov <kirill@...temov.name>
> ---
> include/linux/pagemap.h | 9 +++
> mm/filemap.c | 158 ++++++++++++++++------------------------
> mm/huge_memory.c | 3 +
> mm/khugepaged.c | 4 +-
> mm/memfd.c | 2 +
> mm/migrate.c | 2 +-
> mm/shmem.c | 2 +-
> mm/swap_state.c | 4 +-
> 8 files changed, 81 insertions(+), 103 deletions(-)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index bcf909d0de5f..7d58e4e0b68e 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -333,6 +333,15 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
> mapping_gfp_mask(mapping));
> }
>
> +static inline struct page *find_subpage(struct page *page, pgoff_t offset)
> +{
> + VM_BUG_ON_PAGE(PageTail(page), page);
> + VM_BUG_ON_PAGE(page->index > offset, page);
> + VM_BUG_ON_PAGE(page->index + (1 << compound_order(page)) <= offset,
> + page);
> + return page - page->index + offset;
> +}
> +
> struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);
> struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset);
> unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 5673672fd444..d9161cae11b5 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -279,11 +279,11 @@ EXPORT_SYMBOL(delete_from_page_cache);
> * @pvec: pagevec with pages to delete
> *
> * The function walks over mapping->i_pages and removes pages passed in @pvec
> - * from the mapping. The function expects @pvec to be sorted by page index.
> + * from the mapping. The function expects @pvec to be sorted by page index
> + * and is optimised for it to be dense.
> * It tolerates holes in @pvec (mapping entries at those indices are not
> * modified). The function expects only THP head pages to be present in the
> - * @pvec and takes care to delete all corresponding tail pages from the
> - * mapping as well.
> + * @pvec.
> *
> * The function expects the i_pages lock to be held.
> */
> @@ -292,40 +292,43 @@ static void page_cache_delete_batch(struct address_space *mapping,
> {
> XA_STATE(xas, &mapping->i_pages, pvec->pages[0]->index);
> int total_pages = 0;
> - int i = 0, tail_pages = 0;
> + int i = 0;
> struct page *page;
>
> mapping_set_update(&xas, mapping);
> xas_for_each(&xas, page, ULONG_MAX) {
> - if (i >= pagevec_count(pvec) && !tail_pages)
> + if (i >= pagevec_count(pvec))
> break;
> +
> + /* A swap/dax/shadow entry got inserted? Skip it. */
> if (xa_is_value(page))
> continue;
> - if (!tail_pages) {
> - /*
> - * Some page got inserted in our range? Skip it. We
> - * have our pages locked so they are protected from
> - * being removed.
> - */
> - if (page != pvec->pages[i]) {
> - VM_BUG_ON_PAGE(page->index >
> - pvec->pages[i]->index, page);
> - continue;
> - }
> - WARN_ON_ONCE(!PageLocked(page));
> - if (PageTransHuge(page) && !PageHuge(page))
> - tail_pages = HPAGE_PMD_NR - 1;
> + /*
> + * A page got inserted in our range? Skip it. We have our
> + * pages locked so they are protected from being removed.
> + * If we see a page whose index is higher than ours, it
> + * means our page has been removed, which shouldn't be
> + * possible because we're holding the PageLock.
> + */
> + if (page != pvec->pages[i]) {
> + VM_BUG_ON_PAGE(page->index > pvec->pages[i]->index,
> + page);
> + continue;
> + }
> +
> + WARN_ON_ONCE(!PageLocked(page));
> +
> + if (page->index == xas.xa_index)
> page->mapping = NULL;
> - /*
> - * Leave page->index set: truncation lookup relies
> - * upon it
> - */
> + /* Leave page->index set: truncation lookup relies on it */
> +
> + /*
> + * Move to the next page in the vector if this is a small page
> + * or the index is of the last page in this compound page).
> + */
> + if (page->index + (1UL << compound_order(page)) - 1 ==
> + xas.xa_index)
> i++;
> - } else {
> - VM_BUG_ON_PAGE(page->index + HPAGE_PMD_NR - tail_pages
> - != pvec->pages[i]->index, page);
> - tail_pages--;
> - }
> xas_store(&xas, NULL);
> total_pages++;
> }
> @@ -1491,7 +1494,7 @@ EXPORT_SYMBOL(page_cache_prev_miss);
> struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
> {
> XA_STATE(xas, &mapping->i_pages, offset);
> - struct page *head, *page;
> + struct page *page;
>
> rcu_read_lock();
> repeat:
> @@ -1506,25 +1509,19 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
> if (!page || xa_is_value(page))
> goto out;
>
> - head = compound_head(page);
> - if (!page_cache_get_speculative(head))
> + if (!page_cache_get_speculative(page))
> goto repeat;
>
> - /* The page was split under us? */
> - if (compound_head(page) != head) {
> - put_page(head);
> - goto repeat;
> - }
> -
> /*
> - * Has the page moved?
> + * Has the page moved or been split?
> * This is part of the lockless pagecache protocol. See
> * include/linux/pagemap.h for details.
> */
> if (unlikely(page != xas_reload(&xas))) {
> - put_page(head);
> + put_page(page);
> goto repeat;
> }
> + page = find_subpage(page, offset);
> out:
> rcu_read_unlock();
>
> @@ -1706,7 +1703,6 @@ unsigned find_get_entries(struct address_space *mapping,
>
> rcu_read_lock();
> xas_for_each(&xas, page, ULONG_MAX) {
> - struct page *head;
> if (xas_retry(&xas, page))
> continue;
> /*
> @@ -1717,17 +1713,13 @@ unsigned find_get_entries(struct address_space *mapping,
> if (xa_is_value(page))
> goto export;
>
> - head = compound_head(page);
> - if (!page_cache_get_speculative(head))
> + if (!page_cache_get_speculative(page))
> goto retry;
>
> - /* The page was split under us? */
> - if (compound_head(page) != head)
> - goto put_page;
> -
> - /* Has the page moved? */
> + /* Has the page moved or been split? */
> if (unlikely(page != xas_reload(&xas)))
> goto put_page;
> + page = find_subpage(page, xas.xa_index);
>
> export:
> indices[ret] = xas.xa_index;
> @@ -1736,7 +1728,7 @@ unsigned find_get_entries(struct address_space *mapping,
> break;
> continue;
> put_page:
> - put_page(head);
> + put_page(page);
> retry:
> xas_reset(&xas);
> }
> @@ -1778,33 +1770,27 @@ unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
>
> rcu_read_lock();
> xas_for_each(&xas, page, end) {
> - struct page *head;
> if (xas_retry(&xas, page))
> continue;
> /* Skip over shadow, swap and DAX entries */
> if (xa_is_value(page))
> continue;
>
> - head = compound_head(page);
> - if (!page_cache_get_speculative(head))
> + if (!page_cache_get_speculative(page))
> goto retry;
>
> - /* The page was split under us? */
> - if (compound_head(page) != head)
> - goto put_page;
> -
> - /* Has the page moved? */
> + /* Has the page moved or been split? */
> if (unlikely(page != xas_reload(&xas)))
> goto put_page;
>
> - pages[ret] = page;
> + pages[ret] = find_subpage(page, xas.xa_index);
> if (++ret == nr_pages) {
> *start = page->index + 1;
> goto out;
> }
> continue;
> put_page:
> - put_page(head);
> + put_page(page);
> retry:
> xas_reset(&xas);
> }
> @@ -1849,7 +1835,6 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
>
> rcu_read_lock();
> for (page = xas_load(&xas); page; page = xas_next(&xas)) {
> - struct page *head;
> if (xas_retry(&xas, page))
> continue;
> /*
> @@ -1859,24 +1844,19 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
> if (xa_is_value(page))
> break;
>
> - head = compound_head(page);
> - if (!page_cache_get_speculative(head))
> + if (!page_cache_get_speculative(page))
> goto retry;
>
> - /* The page was split under us? */
> - if (compound_head(page) != head)
> - goto put_page;
> -
> - /* Has the page moved? */
> + /* Has the page moved or been split? */
> if (unlikely(page != xas_reload(&xas)))
> goto put_page;
>
> - pages[ret] = page;
> + pages[ret] = find_subpage(page, xas.xa_index);
> if (++ret == nr_pages)
> break;
> continue;
> put_page:
> - put_page(head);
> + put_page(page);
> retry:
> xas_reset(&xas);
> }
> @@ -1912,7 +1892,6 @@ unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
>
> rcu_read_lock();
> xas_for_each_marked(&xas, page, end, tag) {
> - struct page *head;
> if (xas_retry(&xas, page))
> continue;
> /*
> @@ -1923,26 +1902,21 @@ unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
> if (xa_is_value(page))
> continue;
>
> - head = compound_head(page);
> - if (!page_cache_get_speculative(head))
> + if (!page_cache_get_speculative(page))
> goto retry;
>
> - /* The page was split under us? */
> - if (compound_head(page) != head)
> - goto put_page;
> -
> - /* Has the page moved? */
> + /* Has the page moved or been split? */
> if (unlikely(page != xas_reload(&xas)))
> goto put_page;
>
> - pages[ret] = page;
> + pages[ret] = find_subpage(page, xas.xa_index);
> if (++ret == nr_pages) {
> *index = page->index + 1;
> goto out;
> }
> continue;
> put_page:
> - put_page(head);
> + put_page(page);
> retry:
> xas_reset(&xas);
> }
> @@ -1991,7 +1965,6 @@ unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
>
> rcu_read_lock();
> xas_for_each_marked(&xas, page, ULONG_MAX, tag) {
> - struct page *head;
> if (xas_retry(&xas, page))
> continue;
> /*
> @@ -2002,17 +1975,13 @@ unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
> if (xa_is_value(page))
> goto export;
>
> - head = compound_head(page);
> - if (!page_cache_get_speculative(head))
> + if (!page_cache_get_speculative(page))
> goto retry;
>
> - /* The page was split under us? */
> - if (compound_head(page) != head)
> - goto put_page;
> -
> - /* Has the page moved? */
> + /* Has the page moved or been split? */
> if (unlikely(page != xas_reload(&xas)))
> goto put_page;
> + page = find_subpage(page, xas.xa_index);
>
> export:
> indices[ret] = xas.xa_index;
> @@ -2021,7 +1990,7 @@ unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
> break;
> continue;
> put_page:
> - put_page(head);
> + put_page(page);
> retry:
> xas_reset(&xas);
> }
> @@ -2686,7 +2655,7 @@ void filemap_map_pages(struct vm_fault *vmf,
> pgoff_t last_pgoff = start_pgoff;
> unsigned long max_idx;
> XA_STATE(xas, &mapping->i_pages, start_pgoff);
> - struct page *head, *page;
> + struct page *page;
>
> rcu_read_lock();
> xas_for_each(&xas, page, end_pgoff) {
> @@ -2695,24 +2664,19 @@ void filemap_map_pages(struct vm_fault *vmf,
> if (xa_is_value(page))
> goto next;
>
> - head = compound_head(page);
> -
> /*
> * Check for a locked page first, as a speculative
> * reference may adversely influence page migration.
> */
> - if (PageLocked(head))
> + if (PageLocked(page))
> goto next;
> - if (!page_cache_get_speculative(head))
> + if (!page_cache_get_speculative(page))
> goto next;
>
> - /* The page was split under us? */
> - if (compound_head(page) != head)
> - goto skip;
> -
> - /* Has the page moved? */
> + /* Has the page moved or been split? */
> if (unlikely(page != xas_reload(&xas)))
> goto skip;
> + page = find_subpage(page, xas.xa_index);
>
> if (!PageUptodate(page) ||
> PageReadahead(page) ||
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index d4847026d4b1..7008174c033b 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2458,6 +2458,9 @@ static void __split_huge_page(struct page *page, struct list_head *list,
> if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
> shmem_uncharge(head->mapping->host, 1);
> put_page(head + i);
> + } else if (!PageAnon(page)) {
> + __xa_store(&head->mapping->i_pages, head[i].index,
> + head + i, 0);
> }
> }
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 449044378782..7ba7a1e4fa79 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1374,7 +1374,7 @@ static void collapse_shmem(struct mm_struct *mm,
> result = SCAN_FAIL;
> goto xa_locked;
> }
> - xas_store(&xas, new_page + (index % HPAGE_PMD_NR));
> + xas_store(&xas, new_page);
> nr_none++;
> continue;
> }
> @@ -1450,7 +1450,7 @@ static void collapse_shmem(struct mm_struct *mm,
> list_add_tail(&page->lru, &pagelist);
>
> /* Finally, replace with the new page. */
> - xas_store(&xas, new_page + (index % HPAGE_PMD_NR));
> + xas_store(&xas, new_page);
> continue;
> out_unlock:
> unlock_page(page);
> diff --git a/mm/memfd.c b/mm/memfd.c
> index 650e65a46b9c..bccbf7dff050 100644
> --- a/mm/memfd.c
> +++ b/mm/memfd.c
> @@ -39,6 +39,7 @@ static void memfd_tag_pins(struct xa_state *xas)
> xas_for_each(xas, page, ULONG_MAX) {
> if (xa_is_value(page))
> continue;
> + page = find_subpage(page, xas.xa_index);
This should be xas->xa_index.
I fixed this and am trying to test the patch.
Thanks,
Song
> if (page_count(page) - page_mapcount(page) > 1)
> xas_set_mark(xas, MEMFD_TAG_PINNED);
>
> @@ -88,6 +89,7 @@ static int memfd_wait_for_pins(struct address_space *mapping)
> bool clear = true;
> if (xa_is_value(page))
> continue;
> + page = find_subpage(page, xas.xa_index);
> if (page_count(page) - page_mapcount(page) != 1) {
> /*
> * On the last scan, we clean up all those tags
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 412d5fff78d4..8cb55dd69b9c 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -465,7 +465,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
>
> for (i = 1; i < HPAGE_PMD_NR; i++) {
> xas_next(&xas);
> - xas_store(&xas, newpage + i);
> + xas_store(&xas, newpage);
> }
> }
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index c8cdaa012f18..a78d4f05a51f 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -614,7 +614,7 @@ static int shmem_add_to_page_cache(struct page *page,
> if (xas_error(&xas))
> goto unlock;
> next:
> - xas_store(&xas, page + i);
> + xas_store(&xas, page);
> if (++i < nr) {
> xas_next(&xas);
> goto next;
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 85245fdec8d9..eb714165afd2 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -132,7 +132,7 @@ int add_to_swap_cache(struct page *page, swp_entry_t entry, gfp_t gfp)
> for (i = 0; i < nr; i++) {
> VM_BUG_ON_PAGE(xas.xa_index != idx + i, page);
> set_page_private(page + i, entry.val + i);
> - xas_store(&xas, page + i);
> + xas_store(&xas, page);
> xas_next(&xas);
> }
> address_space->nrpages += nr;
> @@ -167,7 +167,7 @@ void __delete_from_swap_cache(struct page *page, swp_entry_t entry)
>
> for (i = 0; i < nr; i++) {
> void *entry = xas_store(&xas, NULL);
> - VM_BUG_ON_PAGE(entry != page + i, entry);
> + VM_BUG_ON_PAGE(entry != page, entry);
> set_page_private(page + i, 0);
> xas_next(&xas);
> }
> --
> 2.20.1
>
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