From db37648cd6ce9b828abd6d49aa3d269926ee7b7d Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Mon, 25 Sep 2006 23:31:24 -0700 Subject: [PATCH] mm: non syncing lock_page() lock_page needs the caller to have a reference on the page->mapping inode due to sync_page, ergo set_page_dirty_lock is obviously buggy according to its comments. Solve it by introducing a new lock_page_nosync which does not do a sync_page. akpm: unpleasant solution to an unpleasant problem. If it goes wrong it could cause great slowdowns while the lock_page() caller waits for kblockd to perform the unplug. And if a filesystem has special sync_page() requirements (none presently do), permanent hangs are possible. otoh, set_page_dirty_lock() is usually (always?) called against userspace pages. They are always up-to-date, so there shouldn't be any pending read I/O against these pages. Signed-off-by: Nick Piggin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'mm/filemap.c') diff --git a/mm/filemap.c b/mm/filemap.c index b9a60c43b61..d5af1cab426 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -488,6 +488,12 @@ struct page *page_cache_alloc_cold(struct address_space *x) EXPORT_SYMBOL(page_cache_alloc_cold); #endif +static int __sleep_on_page_lock(void *word) +{ + io_schedule(); + return 0; +} + /* * In order to wait for pages to become available there must be * waitqueues associated with pages. By using a hash table of @@ -577,6 +583,17 @@ void fastcall __lock_page(struct page *page) } EXPORT_SYMBOL(__lock_page); +/* + * Variant of lock_page that does not require the caller to hold a reference + * on the page's mapping. + */ +void fastcall __lock_page_nosync(struct page *page) +{ + DEFINE_WAIT_BIT(wait, &page->flags, PG_locked); + __wait_on_bit_lock(page_waitqueue(page), &wait, __sleep_on_page_lock, + TASK_UNINTERRUPTIBLE); +} + /** * find_get_page - find and get a page reference * @mapping: the address_space to search -- cgit v1.2.3 From da6052f7b33abe55fbfd7d2213815f58c00a88d4 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Mon, 25 Sep 2006 23:31:35 -0700 Subject: [PATCH] update some mm/ comments Let's try to keep mm/ comments more useful and up to date. This is a start. Signed-off-by: Nick Piggin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'mm/filemap.c') diff --git a/mm/filemap.c b/mm/filemap.c index d5af1cab426..afcdc72b5e9 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -599,8 +599,8 @@ void fastcall __lock_page_nosync(struct page *page) * @mapping: the address_space to search * @offset: the page index * - * A rather lightweight function, finding and getting a reference to a - * hashed page atomically. + * Is there a pagecache struct page at the given (mapping, offset) tuple? + * If yes, increment its refcount and return it; if no, return NULL. */ struct page * find_get_page(struct address_space *mapping, unsigned long offset) { @@ -987,7 +987,7 @@ page_not_up_to_date: /* Get exclusive access to the page ... */ lock_page(page); - /* Did it get unhashed before we got the lock? */ + /* Did it get truncated before we got the lock? */ if (!page->mapping) { unlock_page(page); page_cache_release(page); @@ -1627,7 +1627,7 @@ no_cached_page: page_not_uptodate: lock_page(page); - /* Did it get unhashed while we waited for it? */ + /* Did it get truncated while we waited for it? */ if (!page->mapping) { unlock_page(page); goto err; -- cgit v1.2.3