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Subject[PATCH 3/4] FS-Cache: Use a radix tree to track pages being written rather than a page flag
Date
Use a radix tree attached to struct fscache_cookie to track what pages are
undergoing write, rather than using a page flag.

The radix tree that was resident in struct fscache_object to track pages that
need writing is moved to fscache_cookie. Pages that need writing and pages
that are being written are both held in there. The difference being that the
former are tagged with FSCACHE_COOKIE_PENDING_TAG.

Signed-off-by: David Howells <dhowells@redhat.com>
---
Documentation/filesystems/caching/netfs-api.txt | 88 +++++++++--------------
fs/afs/file.c | 6 +-
fs/afs/write.c | 2 -
fs/fscache/cookie.c | 2 +
fs/fscache/page.c | 77 ++++++++++++++++----
fs/nfs/file.c | 5 +
fs/nfs/fscache.c | 26 ++++---
fs/nfs/fscache.h | 12 +++
include/linux/fscache-cache.h | 5 +
include/linux/fscache.h | 54 ++++++++++----
10 files changed, 172 insertions(+), 105 deletions(-)

diff --git a/Documentation/filesystems/caching/netfs-api.txt b/Documentation/filesystems/caching/netfs-api.txt
index da8f92f..4db125b 100644
--- a/Documentation/filesystems/caching/netfs-api.txt
+++ b/Documentation/filesystems/caching/netfs-api.txt
@@ -640,7 +640,18 @@ Note that pages can't be explicitly deleted from the a data file. The whole
data file must be retired (see the relinquish cookie function below).

Furthermore, note that this does not cancel the asynchronous read or write
-operation started by the read/alloc and write functions.
+operation started by the read/alloc and write functions, so the page
+invalidation and release functions must use:
+
+ bool fscache_check_page_write(struct fscache_cookie *cookie,
+ struct page *page);
+
+to see if a page is being written to the cache, and:
+
+ void fscache_wait_on_page_write(struct fscache_cookie *cookie,
+ struct page *page);
+
+to wait for it to finish if it is.


==========================
@@ -730,52 +741,32 @@ this, the caller should relinquish and retire the cookie they have, and then
acquire a new one.


-============================
-FS-CACHE SPECIFIC PAGE FLAGS
-============================
-
-FS-Cache makes use of two page flags, PG_private_2 and PG_owner_priv_2, for
-its own purpose. The first is given the alternative name PG_fscache and the
-second PG_fscache_write.
-
-FS-Cache uses these flags to keep track of two bits of information per cached
-netfs page:
+===========================
+FS-CACHE SPECIFIC PAGE FLAG
+===========================

- (1) PG_fscache.
+FS-Cache makes use of a page flag, PG_private_2, for its own purpose. This is
+given the alternative name PG_fscache.

- This indicates that the page is known by the cache, and that the cache
- must be informed if the page is going to go away. It's an indication to
- the netfs that the cache has an interest in this page, where an interest
- may be a pointer to it, resources allocated or reserved for it, or I/O in
- progress upon it.
+PG_fscache is used to indicate that the page is known by the cache, and that
+the cache must be informed if the page is going to go away. It's an indication
+to the netfs that the cache has an interest in this page, where an interest may
+be a pointer to it, resources allocated or reserved for it, or I/O in progress
+upon it.

- The netfs can use this information in methods such as releasepage() to
- determine whether it needs to uncache a page or update it.
+The netfs can use this information in methods such as releasepage() to
+determine whether it needs to uncache a page or update it.

- Furthermore, if this bit is set, releasepage() and invalidatepage()
- operations will be called on a page to get rid of it, even if PG_private
- is not set. This allows caching to attempted on a page before
- read_cache_pages() to be called after fscache_read_or_alloc_pages() as
- the former will try and release pages it was given under certain
- circumstances.
+Furthermore, if this bit is set, releasepage() and invalidatepage() operations
+will be called on a page to get rid of it, even if PG_private is not set. This
+allows caching to attempted on a page before read_cache_pages() to be called
+after fscache_read_or_alloc_pages() as the former will try and release pages it
+was given under certain circumstances.

- (2) PG_fscache_write.
+This bit does not overlap with such as PG_private. This means that FS-Cache
+can be used with a filesystem that uses the block buffering code.

- This indicates that the page is being written to disk by the cache, and
- that it cannot be released until completion. Ideally it shouldn't be
- changed until completion either so as to maintain the known state of the
- cache. This cannot be unified with PG_writeback as the page may be being
- written to both the server and the cache at the same time or at different
- times.
-
- This can be used by the netfs to wait for a page to be written out to the
- cache before, say, releasing or invalidating it, or before allowing
- someone to modify it in page_mkwrite(), say.
-
-Neither of these two bits overlaps with such as PG_private. This means that
-FS-Cache can be used with a filesystem that uses the block buffering code.
-
-There are a number of operations defined on these two bits:
+There are a number of operations defined on this flag:

int PageFsCache(struct page *page);
void SetPageFsCache(struct page *page)
@@ -783,18 +774,5 @@ There are a number of operations defined on these two bits:
int TestSetPageFsCache(struct page *page)
int TestClearPageFsCache(struct page *page)

- int PageFsCacheWrite(struct page *page)
- void SetPageFsCacheWrite(struct page *page)
- void ClearPageFsCacheWrite(struct page *page)
- int TestSetPageFsCacheWrite(struct page *page)
- int TestClearPageFsCacheWrite(struct page *page)
-
These functions are bit test, bit set, bit clear, bit test and set and bit
-test and clear operations on PG_fscache and PG_fscache_write.
-
- void wait_on_page_fscache_write(struct page *page)
- void end_page_fscache_write(struct page *page)
-
-The first of these two functions waits uninterruptibly for PG_fscache_write to
-become clear, if it isn't already so. The second clears PG_fscache_write and
-wakes up anyone waiting for it.
+test and clear operations on PG_fscache.
diff --git a/fs/afs/file.c b/fs/afs/file.c
index aeb6cdd..7a1d942 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -299,7 +299,7 @@ static void afs_invalidatepage(struct page *page, unsigned long offset)
#ifdef CONFIG_AFS_FSCACHE
if (PageFsCache(page)) {
struct afs_vnode *vnode = AFS_FS_I(page->mapping->host);
- wait_on_page_fscache_write(page);
+ fscache_wait_on_page_write(vnode->cache, page);
fscache_uncache_page(vnode->cache, page);
ClearPageFsCache(page);
}
@@ -336,12 +336,12 @@ static int afs_releasepage(struct page *page, gfp_t gfp_flags)
* elected to wait */
#ifdef CONFIG_AFS_FSCACHE
if (PageFsCache(page)) {
- if (PageFsCacheWrite(page)) {
+ if (fscache_check_page_write(vnode->cache, page)) {
if (!(gfp_flags & __GFP_WAIT)) {
_leave(" = F [cache busy]");
return 0;
}
- wait_on_page_fscache_write(page);
+ fscache_wait_on_page_write(vnode->cache, page);
}

fscache_uncache_page(vnode->cache, page);
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 7884518..c2e7a7f 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -795,7 +795,7 @@ int afs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
/* wait for the page to be written to the cache before we allow it to
* be modified */
#ifdef CONFIG_AFS_FSCACHE
- wait_on_page_fscache_write(page);
+ fscache_wait_on_page_write(vnode->cache, page);
#endif

_leave(" = 0");
diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index cd9d065..72fd18f 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -102,6 +102,8 @@ struct fscache_cookie *__fscache_acquire_cookie(
cookie->netfs_data = netfs_data;
cookie->flags = 0;

+ INIT_RADIX_TREE(&cookie->stores, GFP_NOFS);
+
switch (cookie->def->type) {
case FSCACHE_COOKIE_TYPE_INDEX:
fscache_stat(&fscache_n_cookie_index);
diff --git a/fs/fscache/page.c b/fs/fscache/page.c
index 512ec2c..2568e0e 100644
--- a/fs/fscache/page.c
+++ b/fs/fscache/page.c
@@ -17,6 +17,47 @@
#include "internal.h"

/*
+ * check to see if a page is being written to the cache
+ */
+bool __fscache_check_page_write(struct fscache_cookie *cookie, struct page *page)
+{
+ void *val;
+
+ rcu_read_lock();
+ val = radix_tree_lookup(&cookie->stores, page->index);
+ rcu_read_unlock();
+
+ return val != NULL;
+}
+EXPORT_SYMBOL(__fscache_check_page_write);
+
+/*
+ * wait for a page to finish being written to the cache
+ */
+void __fscache_wait_on_page_write(struct fscache_cookie *cookie, struct page *page)
+{
+ wait_queue_head_t *wq = bit_waitqueue(&cookie->flags, 0);
+
+ wait_event(*wq, !__fscache_check_page_write(cookie, page));
+}
+EXPORT_SYMBOL(__fscache_wait_on_page_write);
+
+/*
+ * note that a page has finished being written to the cache
+ */
+static void fscache_end_page_write(struct fscache_cookie *cookie, struct page *page)
+{
+ struct page *xpage;
+
+ spin_lock(&cookie->lock);
+ xpage = radix_tree_delete(&cookie->stores, page->index);
+ spin_unlock(&cookie->lock);
+ ASSERT(xpage != NULL);
+
+ wake_up_bit(&cookie->flags, 0);
+}
+
+/*
* actually apply the changed attributes to a cache object
*/
static void fscache_attr_changed_op(struct fscache_operation *op)
@@ -480,6 +521,7 @@ static void fscache_write_op(struct fscache_operation *_op)
struct fscache_storage *op =
container_of(_op, struct fscache_storage, op);
struct fscache_object *object = op->op.object;
+ struct fscache_cookie *cookie = object->cookie;
struct page *page;
unsigned n;
void *results[1];
@@ -487,10 +529,12 @@ static void fscache_write_op(struct fscache_operation *_op)

_enter("{OP%x,%d}", op->op.debug_id, atomic_read(&op->op.usage));

+ spin_lock(&cookie->lock);
spin_lock(&object->lock);

if (!fscache_object_is_active(object)) {
spin_unlock(&object->lock);
+ spin_unlock(&cookie->lock);
_leave("");
return;
}
@@ -499,23 +543,24 @@ static void fscache_write_op(struct fscache_operation *_op)

/* find a page to store */
page = NULL;
- n = radix_tree_gang_lookup(&object->stores, results, 0, 1);
- if (n == 1) {
- page = results[0];
- _debug("gang %d [%lx]", n, page->index);
- if (page->index <= op->store_limit)
- radix_tree_delete(&object->stores, page->index);
- else
- goto superseded;
- } else {
+ n = radix_tree_gang_lookup_tag(&cookie->stores, results, 0, 1,
+ FSCACHE_COOKIE_PENDING_TAG);
+ if (n != 1)
+ goto superseded;
+ page = results[0];
+ _debug("gang %d [%lx]", n, page->index);
+ if (page->index > op->store_limit)
goto superseded;
- }
+
+ radix_tree_tag_clear(&cookie->stores, page->index,
+ FSCACHE_COOKIE_PENDING_TAG);

spin_unlock(&object->lock);
+ spin_unlock(&cookie->lock);

if (page) {
ret = object->cache->ops->write_page(op, page);
- end_page_fscache_write(page);
+ fscache_end_page_write(cookie, page);
page_cache_release(page);
if (ret < 0)
fscache_abort_object(object);
@@ -532,6 +577,7 @@ superseded:
_debug("cease");
clear_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags);
spin_unlock(&object->lock);
+ spin_unlock(&cookie->lock);
_leave("");
}

@@ -609,7 +655,7 @@ int __fscache_write_page(struct fscache_cookie *cookie,

_debug("store limit %llx", (unsigned long long) object->store_limit);

- ret = radix_tree_insert(&object->stores, page->index, page);
+ ret = radix_tree_insert(&cookie->stores, page->index, page);
if (ret < 0) {
if (ret == -EEXIST)
goto already_queued;
@@ -617,9 +663,9 @@ int __fscache_write_page(struct fscache_cookie *cookie,
goto nobufs_unlock_obj;
}

+ radix_tree_tag_set(&cookie->stores, page->index,
+ FSCACHE_COOKIE_PENDING_TAG);
page_cache_get(page);
- if (TestSetPageFsCacheWrite(page))
- BUG();

/* we only want one writer at a time, but we do need to queue new
* writers after exclusive ops */
@@ -656,8 +702,7 @@ already_pending:
return 0;

submit_failed:
- radix_tree_delete(&object->stores, page->index);
- end_page_fscache_write(page);
+ radix_tree_delete(&cookie->stores, page->index);
page_cache_release(page);
ret = -ENOBUFS;
goto nobufs;
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index d3060c4..3523b89 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -456,11 +456,12 @@ static int nfs_release_page(struct page *page, gfp_t gfp)
static int nfs_launder_page(struct page *page)
{
struct inode *inode = page->mapping->host;
+ struct nfs_inode *nfsi = NFS_I(inode);

dfprintk(PAGECACHE, "NFS: launder_page(%ld, %llu)\n",
inode->i_ino, (long long)page_offset(page));

- wait_on_page_fscache_write(page);
+ nfs_fscache_wait_on_page_write(nfsi, page);
return nfs_wb_page(inode, page);
}

@@ -498,7 +499,7 @@ static int nfs_vm_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
(long long)page_offset(page));

/* make sure the cache has finished storing the page */
- wait_on_page_fscache_write(page);
+ nfs_fscache_wait_on_page_write(NFS_I(dentry->d_inode), page);

lock_page(page);
mapping = page->mapping;
diff --git a/fs/nfs/fscache.c b/fs/nfs/fscache.c
index 968cf5d..379be67 100644
--- a/fs/nfs/fscache.c
+++ b/fs/nfs/fscache.c
@@ -337,21 +337,22 @@ void nfs_fscache_reset_inode_cookie(struct inode *inode)
*/
int nfs_fscache_release_page(struct page *page, gfp_t gfp)
{
- if (PageFsCacheWrite(page)) {
+ struct nfs_inode *nfsi = NFS_I(page->mapping->host);
+ struct fscache_cookie *cookie = nfsi->fscache;
+
+ BUG_ON(!cookie);
+
+ if (fscache_check_page_write(cookie, page)) {
if (!(gfp & __GFP_WAIT))
return 0;
- wait_on_page_fscache_write(page);
+ fscache_wait_on_page_write(cookie, page);
}

if (PageFsCache(page)) {
- struct nfs_inode *nfsi = NFS_I(page->mapping->host);
-
- BUG_ON(!nfsi->fscache);
-
dfprintk(FSCACHE, "NFS: fscache releasepage (0x%p/0x%p/0x%p)\n",
- nfsi->fscache, page, nfsi);
+ cookie, page, nfsi);

- fscache_uncache_page(nfsi->fscache, page);
+ fscache_uncache_page(cookie, page);
nfs_add_fscache_stats(page->mapping->host,
NFSIOS_FSCACHE_PAGES_UNCACHED, 1);
}
@@ -366,16 +367,17 @@ int nfs_fscache_release_page(struct page *page, gfp_t gfp)
void __nfs_fscache_invalidate_page(struct page *page, struct inode *inode)
{
struct nfs_inode *nfsi = NFS_I(inode);
+ struct fscache_cookie *cookie = nfsi->fscache;

- BUG_ON(!nfsi->fscache);
+ BUG_ON(!cookie);

dfprintk(FSCACHE, "NFS: fscache invalidatepage (0x%p/0x%p/0x%p)\n",
- nfsi->fscache, page, nfsi);
+ cookie, page, nfsi);

- wait_on_page_fscache_write(page);
+ fscache_wait_on_page_write(cookie, page);

BUG_ON(!PageLocked(page));
- fscache_uncache_page(nfsi->fscache, page);
+ fscache_uncache_page(cookie, page);
nfs_add_fscache_stats(page->mapping->host,
NFSIOS_FSCACHE_PAGES_UNCACHED, 1);
}
diff --git a/fs/nfs/fscache.h b/fs/nfs/fscache.h
index 2d43b67..6e809bb 100644
--- a/fs/nfs/fscache.h
+++ b/fs/nfs/fscache.h
@@ -94,6 +94,16 @@ extern int __nfs_readpages_from_fscache(struct nfs_open_context *,
extern void __nfs_readpage_to_fscache(struct inode *, struct page *, int);

/*
+ * wait for a page to complete writing to the cache
+ */
+static inline void nfs_fscache_wait_on_page_write(struct nfs_inode *nfsi,
+ struct page *page)
+{
+ if (PageFsCache(page))
+ fscache_wait_on_page_write(nfsi->fscache, page);
+}
+
+/*
* release the caching state associated with a page if undergoing complete page
* invalidation
*/
@@ -181,6 +191,8 @@ static inline int nfs_fscache_release_page(struct page *page, gfp_t gfp)
}
static inline void nfs_fscache_invalidate_page(struct page *page,
struct inode *inode) {}
+static inline void nfs_fscache_wait_on_page_write(struct nfs_inode *nfsi,
+ struct page *page) {}

static inline int nfs_readpage_from_fscache(struct nfs_open_context *ctx,
struct inode *inode,
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 0410bd9..84d3532 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -301,6 +301,9 @@ struct fscache_cookie {
const struct fscache_cookie_def *def; /* definition */
struct fscache_cookie *parent; /* parent of this entry */
void *netfs_data; /* back pointer to netfs */
+ struct radix_tree_root stores; /* pages to be stored on this cookie */
+#define FSCACHE_COOKIE_PENDING_TAG 0 /* pages tag: pending write to cache */
+
unsigned long flags;
#define FSCACHE_COOKIE_LOOKING_UP 0 /* T if non-index cookie being looked up still */
#define FSCACHE_COOKIE_CREATING 1 /* T if non-index object being created still */
@@ -370,7 +373,6 @@ struct fscache_object {
struct list_head dependents; /* FIFO of dependent objects */
struct list_head dep_link; /* link in parent's dependents list */
struct list_head pending_ops; /* unstarted operations on this object */
- struct radix_tree_root stores; /* data to be stored */
pgoff_t store_limit; /* current storage limit */
};

@@ -407,7 +409,6 @@ void fscache_object_init(struct fscache_object *object,
INIT_LIST_HEAD(&object->dependents);
INIT_LIST_HEAD(&object->dep_link);
INIT_LIST_HEAD(&object->pending_ops);
- INIT_RADIX_TREE(&object->stores, GFP_NOFS);
object->n_children = 0;
object->n_ops = object->n_in_progress = object->n_exclusive = 0;
object->events = object->event_mask = 0;
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 006c919..6d8ee46 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -42,20 +42,6 @@
#define TestSetPageFsCache(page) TestSetPagePrivate2((page))
#define TestClearPageFsCache(page) TestClearPagePrivate2((page))

-/*
- * overload PG_owner_priv_2 to give us PG_fscache_write - this is used to
- * indicate that a page is currently being written to a local disk cache
- */
-#define PageFsCacheWrite(page) PageOwnerPriv2((page))
-#define SetPageFsCacheWrite(page) SetPageOwnerPriv2((page))
-#define ClearPageFsCacheWrite(page) ClearPageOwnerPriv2((page))
-#define TestSetPageFsCacheWrite(page) TestSetPageOwnerPriv2((page))
-#define TestClearPageFsCacheWrite(page) TestClearPageOwnerPriv2((page))
-
-#define wait_on_page_fscache_write(page) wait_on_page_owner_priv_2((page))
-#define end_page_fscache_write(page) end_page_owner_priv_2((page))
-
-
/* pattern used to fill dead space in an index entry */
#define FSCACHE_INDEX_DEADFILL_PATTERN 0x79

@@ -214,6 +200,8 @@ extern int __fscache_read_or_alloc_pages(struct fscache_cookie *,
extern int __fscache_alloc_page(struct fscache_cookie *, struct page *, gfp_t);
extern int __fscache_write_page(struct fscache_cookie *, struct page *, gfp_t);
extern void __fscache_uncache_page(struct fscache_cookie *, struct page *);
+extern bool __fscache_check_page_write(struct fscache_cookie *, struct page *);
+extern void __fscache_wait_on_page_write(struct fscache_cookie *, struct page *);

/**
* fscache_register_netfs - Register a filesystem as desiring caching services
@@ -589,4 +577,42 @@ void fscache_uncache_page(struct fscache_cookie *cookie,
__fscache_uncache_page(cookie, page);
}

+/**
+ * fscache_check_page_write - Ask if a page is being writing to the cache
+ * @cookie: The cookie representing the cache object
+ * @page: The netfs page that is being cached.
+ *
+ * Ask the cache if a page is being written to the cache.
+ *
+ * See Documentation/filesystems/caching/netfs-api.txt for a complete
+ * description.
+ */
+static inline
+bool fscache_check_page_write(struct fscache_cookie *cookie,
+ struct page *page)
+{
+ if (fscache_cookie_valid(cookie))
+ return __fscache_check_page_write(cookie, page);
+ return false;
+}
+
+/**
+ * fscache_wait_on_page_write - Wait for a page to complete writing to the cache
+ * @cookie: The cookie representing the cache object
+ * @page: The netfs page that is being cached.
+ *
+ * Ask the cache to wake us up when a page is no longer being written to the
+ * cache.
+ *
+ * See Documentation/filesystems/caching/netfs-api.txt for a complete
+ * description.
+ */
+static inline
+void fscache_wait_on_page_write(struct fscache_cookie *cookie,
+ struct page *page)
+{
+ if (fscache_cookie_valid(cookie))
+ __fscache_wait_on_page_write(cookie, page);
+}
+
#endif /* _LINUX_FSCACHE_H */


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