| Message ID | 20200910183318.20139-8-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Return head pages from find_*_entry | expand |
On Thu, Sep 10, 2020 at 07:33:17PM +0100, Matthew Wilcox (Oracle) wrote: > Convert shmem_getpage_gfp() (the only remaining caller of > find_lock_entry()) to cope with a head page being returned instead of > the subpage for the index. This version was buggy. Apparently I was too focused on running the test suite against XFS and neglected to run it against tmpfs, which crashed instantly. Here's the patch I should have sent. commit 7bfa655881da76f3386e6d4c07e38a165b4a6ca8 Author: Matthew Wilcox (Oracle) <willy@infradead.org> Date: Sun Aug 2 07:22:34 2020 -0400 mm/shmem: Return head page from find_lock_entry Convert shmem_getpage_gfp() (the only remaining caller of find_lock_entry()) to cope with a head page being returned instead of the subpage for the index. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 905a64030647..f374618b2c93 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -371,6 +371,15 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping, mapping_gfp_mask(mapping)); } +/* Does this page contain this index? */ +static inline bool thp_contains(struct page *head, pgoff_t index) +{ + /* HugeTLBfs indexes the page cache in units of hpage_size */ + if (PageHuge(head)) + return head->index == index; + return page_index(head) == (index & ~(thp_nr_pages(head) - 1UL)); +} + /* * Given the page we found in the page cache, return the page corresponding * to this index in the file diff --git a/mm/filemap.c b/mm/filemap.c index 2f134383b0ae..453535170b8d 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1614,37 +1614,34 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t index) } /** - * find_lock_entry - locate, pin and lock a page cache entry - * @mapping: the address_space to search - * @offset: the page cache index + * find_lock_entry - Locate and lock a page cache entry. + * @mapping: The address_space to search. + * @index: The page cache index. * - * Looks up the page cache slot at @mapping & @offset. If there is a - * page cache page, it is returned locked and with an increased - * refcount. + * Looks up the page at @mapping & @index. If there is a page in the + * cache, the head page is returned locked and with an increased refcount. * * If the slot holds a shadow entry of a previously evicted page, or a * swap entry from shmem/tmpfs, it is returned. * - * find_lock_entry() may sleep. - * - * Return: the found page or shadow entry, %NULL if nothing is found. + * Context: May sleep. + * Return: The head page or shadow entry, %NULL if nothing is found. */ -struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset) +struct page *find_lock_entry(struct address_space *mapping, pgoff_t index) { struct page *page; repeat: - page = find_get_entry(mapping, offset); + page = find_get_entry(mapping, index); if (page && !xa_is_value(page)) { lock_page(page); /* Has the page been truncated? */ - if (unlikely(page_mapping(page) != mapping)) { + if (unlikely(page->mapping != mapping)) { unlock_page(page); put_page(page); goto repeat; } - page = find_subpage(page, offset); - VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page); + VM_BUG_ON_PAGE(!thp_contains(page, index), page); } return page; } diff --git a/mm/shmem.c b/mm/shmem.c index 271548ca20f3..58bc9e326d0d 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1822,6 +1822,8 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, return error; } + if (page) + hindex = page->index; if (page && sgp == SGP_WRITE) mark_page_accessed(page); @@ -1832,11 +1834,10 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, unlock_page(page); put_page(page); page = NULL; + hindex = index; } - if (page || sgp == SGP_READ) { - *pagep = page; - return 0; - } + if (page || sgp == SGP_READ) + goto out; /* * Fast cache lookup did not find it: @@ -1961,14 +1962,13 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, * it now, lest undo on failure cancel our earlier guarantee. */ if (sgp != SGP_WRITE && !PageUptodate(page)) { - struct page *head = compound_head(page); int i; - for (i = 0; i < compound_nr(head); i++) { - clear_highpage(head + i); - flush_dcache_page(head + i); + for (i = 0; i < compound_nr(page); i++) { + clear_highpage(page + i); + flush_dcache_page(page + i); } - SetPageUptodate(head); + SetPageUptodate(page); } /* Perhaps the file has been truncated since we checked */ @@ -1984,6 +1984,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, error = -EINVAL; goto unlock; } +out: *pagep = page + index - hindex; return 0;
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 905a64030647..f374618b2c93 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -371,6 +371,15 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping, mapping_gfp_mask(mapping)); } +/* Does this page contain this index? */ +static inline bool thp_contains(struct page *head, pgoff_t index) +{ + /* HugeTLBfs indexes the page cache in units of hpage_size */ + if (PageHuge(head)) + return head->index == index; + return page_index(head) == (index & ~(thp_nr_pages(head) - 1UL)); +} + /* * Given the page we found in the page cache, return the page corresponding * to this index in the file diff --git a/mm/filemap.c b/mm/filemap.c index 2f134383b0ae..453535170b8d 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1614,37 +1614,34 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t index) } /** - * find_lock_entry - locate, pin and lock a page cache entry - * @mapping: the address_space to search - * @offset: the page cache index + * find_lock_entry - Locate and lock a page cache entry. + * @mapping: The address_space to search. + * @index: The page cache index. * - * Looks up the page cache slot at @mapping & @offset. If there is a - * page cache page, it is returned locked and with an increased - * refcount. + * Looks up the page at @mapping & @index. If there is a page in the + * cache, the head page is returned locked and with an increased refcount. * * If the slot holds a shadow entry of a previously evicted page, or a * swap entry from shmem/tmpfs, it is returned. * - * find_lock_entry() may sleep. - * - * Return: the found page or shadow entry, %NULL if nothing is found. + * Context: May sleep. + * Return: The head page or shadow entry, %NULL if nothing is found. */ -struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset) +struct page *find_lock_entry(struct address_space *mapping, pgoff_t index) { struct page *page; repeat: - page = find_get_entry(mapping, offset); + page = find_get_entry(mapping, index); if (page && !xa_is_value(page)) { lock_page(page); /* Has the page been truncated? */ - if (unlikely(page_mapping(page) != mapping)) { + if (unlikely(page->mapping != mapping)) { unlock_page(page); put_page(page); goto repeat; } - page = find_subpage(page, offset); - VM_BUG_ON_PAGE(page_to_pgoff(page) != offset, page); + VM_BUG_ON_PAGE(!thp_contains(page, index), page); } return page; } diff --git a/mm/shmem.c b/mm/shmem.c index 271548ca20f3..d2a46ef7df43 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1793,7 +1793,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, struct mm_struct *charge_mm; struct page *page; enum sgp_type sgp_huge = sgp; - pgoff_t hindex = index; + pgoff_t hindex; int error; int once = 0; int alloced = 0; @@ -1833,10 +1833,8 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, put_page(page); page = NULL; } - if (page || sgp == SGP_READ) { - *pagep = page; - return 0; - } + if (page || sgp == SGP_READ) + goto out; /* * Fast cache lookup did not find it: @@ -1961,14 +1959,13 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, * it now, lest undo on failure cancel our earlier guarantee. */ if (sgp != SGP_WRITE && !PageUptodate(page)) { - struct page *head = compound_head(page); int i; - for (i = 0; i < compound_nr(head); i++) { - clear_highpage(head + i); - flush_dcache_page(head + i); + for (i = 0; i < compound_nr(page); i++) { + clear_highpage(page + i); + flush_dcache_page(page + i); } - SetPageUptodate(head); + SetPageUptodate(page); } /* Perhaps the file has been truncated since we checked */ @@ -1984,7 +1981,8 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, error = -EINVAL; goto unlock; } - *pagep = page + index - hindex; +out: + *pagep = page + index - page->index; return 0; /*
Convert shmem_getpage_gfp() (the only remaining caller of find_lock_entry()) to cope with a head page being returned instead of the subpage for the index. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- include/linux/pagemap.h | 9 +++++++++ mm/filemap.c | 25 +++++++++++-------------- mm/shmem.c | 20 +++++++++----------- 3 files changed, 29 insertions(+), 25 deletions(-)