From d08b3851da41d0ee60851f2c75b118e1f7a5fc89 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 25 Sep 2006 23:30:57 -0700 Subject: [PATCH] mm: tracking shared dirty pages Tracking of dirty pages in shared writeable mmap()s. The idea is simple: write protect clean shared writeable pages, catch the write-fault, make writeable and set dirty. On page write-back clean all the PTE dirty bits and write protect them once again. The implementation is a tad harder, mainly because the default backing_dev_info capabilities were too loosely maintained. Hence it is not enough to test the backing_dev_info for cap_account_dirty. The current heuristic is as follows, a VMA is eligible when: - its shared writeable (vm_flags & (VM_WRITE|VM_SHARED)) == (VM_WRITE|VM_SHARED) - it is not a 'special' mapping (vm_flags & (VM_PFNMAP|VM_INSERTPAGE)) == 0 - the backing_dev_info is cap_account_dirty mapping_cap_account_dirty(vma->vm_file->f_mapping) - f_op->mmap() didn't change the default page protection Page from remap_pfn_range() are explicitly excluded because their COW semantics are already horrid enough (see vm_normal_page() in do_wp_page()) and because they don't have a backing store anyway. mprotect() is taught about the new behaviour as well. However it overrides the last condition. Cleaning the pages on write-back is done with page_mkclean() a new rmap call. It can be called on any page, but is currently only implemented for mapped pages, if the page is found the be of a VMA that accounts dirty pages it will also wrprotect the PTE. Finally, in fs/buffers.c:try_to_free_buffers(); remove clear_page_dirty() from under ->private_lock. This seems to be safe, since ->private_lock is used to serialize access to the buffers, not the page itself. This is needed because clear_page_dirty() will call into page_mkclean() and would thereby violate locking order. [dhowells@redhat.com: Provide a page_mkclean() implementation for NOMMU] Signed-off-by: Peter Zijlstra Cc: Hugh Dickins Signed-off-by: David Howells Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page-writeback.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) (limited to 'mm/page-writeback.c') diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 77a0bc4..1c87430 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #include #include @@ -550,7 +551,7 @@ int do_writepages(struct address_space *mapping, struct writeback_control *wbc) return 0; wbc->for_writepages = 1; if (mapping->a_ops->writepages) - ret = mapping->a_ops->writepages(mapping, wbc); + ret = mapping->a_ops->writepages(mapping, wbc); else ret = generic_writepages(mapping, wbc); wbc->for_writepages = 0; @@ -712,9 +713,15 @@ int test_clear_page_dirty(struct page *page) radix_tree_tag_clear(&mapping->page_tree, page_index(page), PAGECACHE_TAG_DIRTY); - if (mapping_cap_account_dirty(mapping)) - __dec_zone_page_state(page, NR_FILE_DIRTY); write_unlock_irqrestore(&mapping->tree_lock, flags); + /* + * We can continue to use `mapping' here because the + * page is locked, which pins the address_space + */ + if (mapping_cap_account_dirty(mapping)) { + page_mkclean(page); + dec_zone_page_state(page, NR_FILE_DIRTY); + } return 1; } write_unlock_irqrestore(&mapping->tree_lock, flags); @@ -744,8 +751,10 @@ int clear_page_dirty_for_io(struct page *page) if (mapping) { if (TestClearPageDirty(page)) { - if (mapping_cap_account_dirty(mapping)) + if (mapping_cap_account_dirty(mapping)) { + page_mkclean(page); dec_zone_page_state(page, NR_FILE_DIRTY); + } return 1; } return 0; -- cgit v1.1