Re: [PATCH v8 06/63] btrfs: Use filemap_range_has_page()

[David Sterba]

On Tue, Mar 06, 2018 at 11:23:16AM -0800, Matthew Wilcox wrote:
> From: Matthew Wilcox 
> 
> The current implementation of btrfs_page_exists_in_range() gives the
> wrong answer if the workingset code has stored a shadow entry in the
> page cache.  The filemap_range_has_page() function does not have this
> problem, and it's shared code, so use it instead.

I'm going to merge this patch. btrfs_page_exists_in_range was full of
bugs from the beginning so I'm more than happy to use the shared one.
Thanks.
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[PATCH v8 06/63] btrfs: Use filemap_range_has_page()

[Matthew Wilcox]

From: Matthew Wilcox 

The current implementation of btrfs_page_exists_in_range() gives the
wrong answer if the workingset code has stored a shadow entry in the
page cache.  The filemap_range_has_page() function does not have this
problem, and it's shared code, so use it instead.

Signed-off-by: Matthew Wilcox 
---
 fs/btrfs/btrfs_inode.h |  6 -
 fs/btrfs/inode.c   | 70 --
 2 files changed, 5 insertions(+), 71 deletions(-)

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index f527e99c9f8d..078a53e01ece 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -364,6 +364,10 @@ static inline void btrfs_print_data_csum_error(struct 
btrfs_inode *inode,
logical_start, csum, csum_expected, mirror_num);
 }
 
-bool btrfs_page_exists_in_range(struct inode *inode, loff_t start, loff_t end);
+static inline bool btrfs_page_exists_in_range(struct inode *inode,
+   loff_t start, loff_t end)
+{
+   return filemap_range_has_page(inode->i_mapping, start, end);
+}
 
 #endif
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 1f5b93ecffca..3340de232944 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7476,76 +7476,6 @@ noinline int can_nocow_extent(struct inode *inode, u64 
offset, u64 *len,
return ret;
 }
 
-bool btrfs_page_exists_in_range(struct inode *inode, loff_t start, loff_t end)
-{
-   struct radix_tree_root *root = >i_mapping->page_tree;
-   bool found = false;
-   void **pagep = NULL;
-   struct page *page = NULL;
-   unsigned long start_idx;
-   unsigned long end_idx;
-
-   start_idx = start >> PAGE_SHIFT;
-
-   /*
-* end is the last byte in the last page.  end == start is legal
-*/
-   end_idx = end >> PAGE_SHIFT;
-
-   rcu_read_lock();
-
-   /* Most of the code in this while loop is lifted from
-* find_get_page.  It's been modified to begin searching from a
-* page and return just the first page found in that range.  If the
-* found idx is less than or equal to the end idx then we know that
-* a page exists.  If no pages are found or if those pages are
-* outside of the range then we're fine (yay!) */
-   while (page == NULL &&
-  radix_tree_gang_lookup_slot(root, , NULL, start_idx, 1)) {
-   page = radix_tree_deref_slot(pagep);
-   if (unlikely(!page))
-   break;
-
-   if (radix_tree_exception(page)) {
-   if (radix_tree_deref_retry(page)) {
-   page = NULL;
-   continue;
-   }
-   /*
-* Otherwise, shmem/tmpfs must be storing a swap entry
-* here as an exceptional entry: so return it without
-* attempting to raise page count.
-*/
-   page = NULL;
-   break; /* TODO: Is this relevant for this use case? */
-   }
-
-   if (!page_cache_get_speculative(page)) {
-   page = NULL;
-   continue;
-   }
-
-   /*
-* Has the page moved?
-* This is part of the lockless pagecache protocol. See
-* include/linux/pagemap.h for details.
-*/
-   if (unlikely(page != *pagep)) {
-   put_page(page);
-   page = NULL;
-   }
-   }
-
-   if (page) {
-   if (page->index <= end_idx)
-   found = true;
-   put_page(page);
-   }
-
-   rcu_read_unlock();
-   return found;
-}
-
 static int lock_extent_direct(struct inode *inode, u64 lockstart, u64 lockend,
  struct extent_state **cached_state, int writing)
 {
-- 
2.16.1

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