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* Fwd: Add page_cache_readahead_unbounded
@ 2020-03-20 14:29 Matthew Wilcox
  2020-03-20 15:49 ` [f2fs-dev] " Eric Biggers
  0 siblings, 1 reply; 2+ messages in thread
From: Matthew Wilcox @ 2020-03-20 14:29 UTC (permalink / raw)
  To: linux-ext4, linux-f2fs-devel, Eric Biggers, Theodore Ts'o,
	Jaegeuk Kim, Chao Yu


I'm a little disappointed to have received no feedback on these patches
from those who were involved with creating the ugly situation in the
first place.

There are other ext4/f2fs patches in this patch series for which it
would also be nice to get reviewed-by tags.

----- Forwarded message from Matthew Wilcox <willy@infradead.org> -----

Date: Fri, 20 Mar 2020 07:22:19 -0700
From: Matthew Wilcox <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org,
	linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com,
	ocfs2-devel@oss.oracle.com, linux-xfs@vger.kernel.org, Christoph
	Hellwig <hch@lst.de>, William Kucharski <william.kucharski@oracle.com>
Subject: [PATCH v9 13/25] mm: Add page_cache_readahead_unbounded
X-Mailer: git-send-email 2.21.1

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

ext4 and f2fs have duplicated the guts of the readahead code so
they can read past i_size.  Instead, separate out the guts of the
readahead code so they can call it directly.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
---
 fs/ext4/verity.c        | 35 ++-----------------
 fs/f2fs/data.c          |  2 +-
 fs/f2fs/f2fs.h          |  3 --
 fs/f2fs/verity.c        | 35 ++-----------------
 include/linux/pagemap.h |  3 ++
 mm/readahead.c          | 74 ++++++++++++++++++++++++++++-------------
 6 files changed, 58 insertions(+), 94 deletions(-)

diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c
index dc5ec724d889..dec1244dd062 100644
--- a/fs/ext4/verity.c
+++ b/fs/ext4/verity.c
@@ -342,37 +342,6 @@ static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
 	return desc_size;
 }
 
-/*
- * Prefetch some pages from the file's Merkle tree.
- *
- * This is basically a stripped-down version of __do_page_cache_readahead()
- * which works on pages past i_size.
- */
-static void ext4_merkle_tree_readahead(struct address_space *mapping,
-				       pgoff_t start_index, unsigned long count)
-{
-	LIST_HEAD(pages);
-	unsigned int nr_pages = 0;
-	struct page *page;
-	pgoff_t index;
-	struct blk_plug plug;
-
-	for (index = start_index; index < start_index + count; index++) {
-		page = xa_load(&mapping->i_pages, index);
-		if (!page || xa_is_value(page)) {
-			page = __page_cache_alloc(readahead_gfp_mask(mapping));
-			if (!page)
-				break;
-			page->index = index;
-			list_add(&page->lru, &pages);
-			nr_pages++;
-		}
-	}
-	blk_start_plug(&plug);
-	ext4_mpage_readpages(mapping, &pages, NULL, nr_pages, true);
-	blk_finish_plug(&plug);
-}
-
 static struct page *ext4_read_merkle_tree_page(struct inode *inode,
 					       pgoff_t index,
 					       unsigned long num_ra_pages)
@@ -386,8 +355,8 @@ static struct page *ext4_read_merkle_tree_page(struct inode *inode,
 		if (page)
 			put_page(page);
 		else if (num_ra_pages > 1)
-			ext4_merkle_tree_readahead(inode->i_mapping, index,
-						   num_ra_pages);
+			page_cache_readahead_unbounded(inode->i_mapping, NULL,
+					index, num_ra_pages, 0);
 		page = read_mapping_page(inode->i_mapping, index, NULL);
 	}
 	return page;
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index b27b72107911..8e9aa2254490 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2159,7 +2159,7 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
  * use ->readpage() or do the necessary surgery to decouple ->readpages()
  * from read-ahead.
  */
-int f2fs_mpage_readpages(struct address_space *mapping,
+static int f2fs_mpage_readpages(struct address_space *mapping,
 			struct list_head *pages, struct page *page,
 			unsigned nr_pages, bool is_readahead)
 {
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 5355be6b6755..4a414e06a8af 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -3344,9 +3344,6 @@ int f2fs_reserve_new_block(struct dnode_of_data *dn);
 int f2fs_get_block(struct dnode_of_data *dn, pgoff_t index);
 int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from);
 int f2fs_reserve_block(struct dnode_of_data *dn, pgoff_t index);
-int f2fs_mpage_readpages(struct address_space *mapping,
-			struct list_head *pages, struct page *page,
-			unsigned nr_pages, bool is_readahead);
 struct page *f2fs_get_read_data_page(struct inode *inode, pgoff_t index,
 			int op_flags, bool for_write);
 struct page *f2fs_find_data_page(struct inode *inode, pgoff_t index);
diff --git a/fs/f2fs/verity.c b/fs/f2fs/verity.c
index d7d430a6f130..865c9fb774fb 100644
--- a/fs/f2fs/verity.c
+++ b/fs/f2fs/verity.c
@@ -222,37 +222,6 @@ static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
 	return size;
 }
 
-/*
- * Prefetch some pages from the file's Merkle tree.
- *
- * This is basically a stripped-down version of __do_page_cache_readahead()
- * which works on pages past i_size.
- */
-static void f2fs_merkle_tree_readahead(struct address_space *mapping,
-				       pgoff_t start_index, unsigned long count)
-{
-	LIST_HEAD(pages);
-	unsigned int nr_pages = 0;
-	struct page *page;
-	pgoff_t index;
-	struct blk_plug plug;
-
-	for (index = start_index; index < start_index + count; index++) {
-		page = xa_load(&mapping->i_pages, index);
-		if (!page || xa_is_value(page)) {
-			page = __page_cache_alloc(readahead_gfp_mask(mapping));
-			if (!page)
-				break;
-			page->index = index;
-			list_add(&page->lru, &pages);
-			nr_pages++;
-		}
-	}
-	blk_start_plug(&plug);
-	f2fs_mpage_readpages(mapping, &pages, NULL, nr_pages, true);
-	blk_finish_plug(&plug);
-}
-
 static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
 					       pgoff_t index,
 					       unsigned long num_ra_pages)
@@ -266,8 +235,8 @@ static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
 		if (page)
 			put_page(page);
 		else if (num_ra_pages > 1)
-			f2fs_merkle_tree_readahead(inode->i_mapping, index,
-						   num_ra_pages);
+			page_cache_readahead_unbounded(inode->i_mapping, NULL,
+					index, num_ra_pages, 0);
 		page = read_mapping_page(inode->i_mapping, index, NULL);
 	}
 	return page;
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 232892d37071..0c25625ed27d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -621,6 +621,9 @@ void page_cache_sync_readahead(struct address_space *, struct file_ra_state *,
 void page_cache_async_readahead(struct address_space *, struct file_ra_state *,
 		struct file *, struct page *, pgoff_t index,
 		unsigned long req_count);
+void page_cache_readahead_unbounded(struct address_space *, struct file *,
+		pgoff_t index, unsigned long nr_to_read,
+		unsigned long lookahead_count);
 
 /*
  * Like add_to_page_cache_locked, but used to add newly allocated pages:
diff --git a/mm/readahead.c b/mm/readahead.c
index a37b68f66233..8ee9036fd681 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -156,40 +156,34 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages,
 		rac->_index++;
 }
 
-/*
- * __do_page_cache_readahead() actually reads a chunk of disk.  It allocates
- * the pages first, then submits them for I/O. This avoids the very bad
- * behaviour which would occur if page allocations are causing VM writeback.
- * We really don't want to intermingle reads and writes like that.
+/**
+ * page_cache_readahead_unbounded - Start unchecked readahead.
+ * @mapping: File address space.
+ * @file: This instance of the open file; used for authentication.
+ * @index: First page index to read.
+ * @nr_to_read: The number of pages to read.
+ * @lookahead_size: Where to start the next readahead.
+ *
+ * This function is for filesystems to call when they want to start
+ * readahead beyond a file's stated i_size.  This is almost certainly
+ * not the function you want to call.  Use page_cache_async_readahead()
+ * or page_cache_sync_readahead() instead.
+ *
+ * Context: File is referenced by caller.  Mutexes may be held by caller.
+ * May sleep, but will not reenter filesystem to reclaim memory.
  */
-void __do_page_cache_readahead(struct address_space *mapping,
-		struct file *filp, pgoff_t index, unsigned long nr_to_read,
+void page_cache_readahead_unbounded(struct address_space *mapping,
+		struct file *file, pgoff_t index, unsigned long nr_to_read,
 		unsigned long lookahead_size)
 {
-	struct inode *inode = mapping->host;
 	LIST_HEAD(page_pool);
-	loff_t isize = i_size_read(inode);
 	gfp_t gfp_mask = readahead_gfp_mask(mapping);
 	struct readahead_control rac = {
 		.mapping = mapping,
-		.file = filp,
+		.file = file,
 		._index = index,
 	};
 	unsigned long i;
-	pgoff_t end_index;	/* The last page we want to read */
-
-	if (isize == 0)
-		return;
-
-	end_index = (isize - 1) >> PAGE_SHIFT;
-	if (index > end_index)
-		return;
-	/* Avoid wrapping to the beginning of the file */
-	if (index + nr_to_read < index)
-		nr_to_read = ULONG_MAX - index + 1;
-	/* Don't read past the page containing the last byte of the file */
-	if (index + nr_to_read >= end_index)
-		nr_to_read = end_index - index + 1;
 
 	/*
 	 * Preallocate as many pages as we will need.
@@ -233,6 +227,38 @@ void __do_page_cache_readahead(struct address_space *mapping,
 	 */
 	read_pages(&rac, &page_pool, false);
 }
+EXPORT_SYMBOL_GPL(page_cache_readahead_unbounded);
+
+/*
+ * __do_page_cache_readahead() actually reads a chunk of disk.  It allocates
+ * the pages first, then submits them for I/O. This avoids the very bad
+ * behaviour which would occur if page allocations are causing VM writeback.
+ * We really don't want to intermingle reads and writes like that.
+ */
+void __do_page_cache_readahead(struct address_space *mapping,
+		struct file *file, pgoff_t index, unsigned long nr_to_read,
+		unsigned long lookahead_size)
+{
+	struct inode *inode = mapping->host;
+	loff_t isize = i_size_read(inode);
+	pgoff_t end_index;	/* The last page we want to read */
+
+	if (isize == 0)
+		return;
+
+	end_index = (isize - 1) >> PAGE_SHIFT;
+	if (index > end_index)
+		return;
+	/* Avoid wrapping to the beginning of the file */
+	if (index + nr_to_read < index)
+		nr_to_read = ULONG_MAX - index + 1;
+	/* Don't read past the page containing the last byte of the file */
+	if (index + nr_to_read >= end_index)
+		nr_to_read = end_index - index + 1;
+
+	page_cache_readahead_unbounded(mapping, file, index, nr_to_read,
+			lookahead_size);
+}
 
 /*
  * Chunk the readahead into 2 megabyte units, so that we don't pin too much
-- 
2.25.1


----- End forwarded message -----

^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [f2fs-dev] Fwd: Add page_cache_readahead_unbounded
  2020-03-20 14:29 Fwd: Add page_cache_readahead_unbounded Matthew Wilcox
@ 2020-03-20 15:49 ` " Eric Biggers
  0 siblings, 0 replies; 2+ messages in thread
From: Eric Biggers @ 2020-03-20 15:49 UTC (permalink / raw)
  To: Matthew Wilcox
  Cc: linux-ext4, linux-f2fs-devel, Theodore Ts'o, Jaegeuk Kim, Chao Yu

Hi Matthew,

On Fri, Mar 20, 2020 at 07:29:32AM -0700, Matthew Wilcox wrote:
> 
> I'm a little disappointed to have received no feedback on these patches
> from those who were involved with creating the ugly situation in the
> first place.
> 
> There are other ext4/f2fs patches in this patch series for which it
> would also be nice to get reviewed-by tags.
> 
> ----- Forwarded message from Matthew Wilcox <willy@infradead.org> -----
> 
> Date: Fri, 20 Mar 2020 07:22:19 -0700
> From: Matthew Wilcox <willy@infradead.org>
> To: Andrew Morton <akpm@linux-foundation.org>
> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
> 	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
> 	linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org,
> 	linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org,
> 	linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com,
> 	ocfs2-devel@oss.oracle.com, linux-xfs@vger.kernel.org, Christoph
> 	Hellwig <hch@lst.de>, William Kucharski <william.kucharski@oracle.com>
> Subject: [PATCH v9 13/25] mm: Add page_cache_readahead_unbounded
> X-Mailer: git-send-email 2.21.1
> 
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> ext4 and f2fs have duplicated the guts of the readahead code so
> they can read past i_size.  Instead, separate out the guts of the
> readahead code so they can call it directly.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: William Kucharski <william.kucharski@oracle.com>

I actually did look at this patch last month and it looked fine.  Thanks for
doing this.

To be clear, we'd be fine with maintaining filesystem-specific code that does
the setup necessary to call ext4_mpage_readpages() and f2fs_mpage_readpages()
properly.  And that was the original intent, so that nothing would leak into the
VFS.  But I understand that the new readahead calling convention is different
and a bit more complex, and it's annoying to have multiple callers.  So if
page_cache_readahead_unbounded() makes things easier for you, it's fine with me.

I'll take a closer look at your v9 series today and provide Reviewed-by on this
patch and others.  Sorry for not doing so earlier.

Thanks!

- Eric

^ permalink raw reply	[flat|nested] 2+ messages in thread

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2020-03-20 14:29 Fwd: Add page_cache_readahead_unbounded Matthew Wilcox
2020-03-20 15:49 ` [f2fs-dev] " Eric Biggers

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