[Linux-cachefs] [RFC PATCH] ceph: Write through cache support based on fscache

[Li Wang]

Currently, fscache only plays as read cache for ceph, this patch
enables it plays as the write through cache as well. 

A small trick to be discussed: if the writing to OSD finishes before
the writing to fscache, the fscache writing is cancelled to avoid 
slow down the writepages() process.

Signed-off-by: Min Chen <minchen at ubuntukylin.com>
Signed-off-by: Li Wang <liwang at ubuntukylin.com>
Signed-off-by: Yunchuan Wen <yunchuanwen at ubuntukylin.com>
---
 fs/ceph/addr.c  |   10 +++++++---
 fs/ceph/cache.c |   29 +++++++++++++++++++++++++++++
 fs/ceph/cache.h |   13 +++++++++++++
 3 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 6df8bd4..2465c49 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -506,7 +506,7 @@ static int writepage_nounlock(struct page *page, struct writeback_control *wbc)
 	    CONGESTION_ON_THRESH(fsc->mount_options->congestion_kb))
 		set_bdi_congested(&fsc->backing_dev_info, BLK_RW_ASYNC);
 
-	ceph_readpage_to_fscache(inode, page);
+	ceph_writepage_to_fscache(inode, page);
 
 	set_page_writeback(page);
 	err = ceph_osdc_writepages(osdc, ceph_vino(inode),
@@ -634,6 +634,7 @@ static void writepages_finish(struct ceph_osd_request *req,
 		if ((issued & (CEPH_CAP_FILE_CACHE|CEPH_CAP_FILE_LAZYIO)) == 0)
 			generic_error_remove_page(inode->i_mapping, page);
 
+		ceph_maybe_release_fscache_page(inode, page);
 		unlock_page(page);
 	}
 	dout("%p wrote+cleaned %d pages\n", inode, wrote);
@@ -746,7 +747,7 @@ retry:
 
 	while (!done && index <= end) {
 		int num_ops = do_sync ? 2 : 1;
-		unsigned i;
+		unsigned i, j;
 		int first;
 		pgoff_t next;
 		int pvec_pages, locked_pages;
@@ -894,7 +895,6 @@ get_more_pages:
 		if (!locked_pages)
 			goto release_pvec_pages;
 		if (i) {
-			int j;
 			BUG_ON(!locked_pages || first < 0);
 
 			if (pvec_pages && i == pvec_pages &&
@@ -924,6 +924,10 @@ get_more_pages:
 
 		osd_req_op_extent_osd_data_pages(req, 0, pages, len, 0,
 							!!pool, false);
+		for (j = 0; j < locked_pages; j++) {
+			struct page *page = pages[j];
+			ceph_writepage_to_fscache(inode, page);
+		}
 
 		pages = NULL;	/* request message now owns the pages array */
 		pool = NULL;
diff --git a/fs/ceph/cache.c b/fs/ceph/cache.c
index 6bfe65e..6f928c4 100644
--- a/fs/ceph/cache.c
+++ b/fs/ceph/cache.c
@@ -320,6 +320,24 @@ void ceph_readpage_to_fscache(struct inode *inode, struct page *page)
 		 fscache_uncache_page(ci->fscache, page);
 }
 
+void ceph_writepage_to_fscache(struct inode *inode, struct page *page)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	int ret;
+
+	if (!cache_valid(ci))
+		return;
+
+	if (!PageFsCache(page)) {
+		if (fscache_alloc_page(ci->fscache, page, GFP_KERNEL))
+			return;
+	}
+
+	if (fscache_write_page(ci->fscache, page, GFP_KERNEL))
+		fscache_uncache_page(ci->fscache, page);
+}
+
+
 void ceph_invalidate_fscache_page(struct inode* inode, struct page *page)
 {
 	struct ceph_inode_info *ci = ceph_inode(inode);
@@ -328,6 +346,17 @@ void ceph_invalidate_fscache_page(struct inode* inode, struct page *page)
 	fscache_uncache_page(ci->fscache, page);
 }
 
+void ceph_maybe_release_fscache_page(struct inode *inode, struct page *page)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+
+	if (PageFsCache(page)) {
+		if (!fscache_check_page_write(ci->fscache, page))
+			fscache_maybe_release_page(ci->fscache,
+						   page, GFP_KERNEL);
+	}
+}
+
 void ceph_fscache_unregister_fs(struct ceph_fs_client* fsc)
 {
 	if (fsc->revalidate_wq)
diff --git a/fs/ceph/cache.h b/fs/ceph/cache.h
index ba94940..aa02b7a 100644
--- a/fs/ceph/cache.h
+++ b/fs/ceph/cache.h
@@ -45,7 +45,9 @@ int ceph_readpages_from_fscache(struct inode *inode,
 				struct list_head *pages,
 				unsigned *nr_pages);
 void ceph_readpage_to_fscache(struct inode *inode, struct page *page);
+void ceph_writepage_to_fscache(struct inode *inode, struct page *page);
 void ceph_invalidate_fscache_page(struct inode* inode, struct page *page);
+void ceph_maybe_release_fscache_page(struct inode *inode, struct page *page);
 void ceph_queue_revalidate(struct inode *inode);
 
 static inline void ceph_fscache_invalidate(struct inode *inode)
@@ -127,6 +129,11 @@ static inline void ceph_readpage_to_fscache(struct inode *inode,
 {
 }
 
+static inline void ceph_writepage_to_fscache(struct inode *inode,
+					     struct page *page)
+{
+}
+
 static inline void ceph_fscache_invalidate(struct inode *inode)
 {
 }
@@ -140,6 +147,12 @@ static inline void ceph_fscache_unregister_inode_cookie(struct ceph_inode_info*
 {
 }
 
+
+static inline void ceph_maybe_release_fscache_page(struct inode *inode,
+						   struct page *page)
+{
+}
+
 static inline int ceph_release_fscache_page(struct page *page, gfp_t gfp)
 {
 	return 1;
-- 
1.7.9.5