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NFS: Refactor nfs_lock_and_join_requests()
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Refactor nfs_lock_and_join_requests() in order to separate out the
subrequest merging into its own function nfs_lock_and_join_group()
that can be used by O_DIRECT.

Signed-off-by: Trond Myklebust <[email protected]>
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Trond Myklebust committed Apr 1, 2020
1 parent 44a65a0 commit e00ed89
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Showing 3 changed files with 123 additions and 68 deletions.
26 changes: 24 additions & 2 deletions fs/nfs/pagelist.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -130,6 +130,25 @@ nfs_async_iocounter_wait(struct rpc_task *task, struct nfs_lock_context *l_ctx)
}
EXPORT_SYMBOL_GPL(nfs_async_iocounter_wait);

/*
* nfs_page_lock_head_request - page lock the head of the page group
* @req: any member of the page group
*/
struct nfs_page *
nfs_page_group_lock_head(struct nfs_page *req)
{
struct nfs_page *head = req->wb_head;

while (!nfs_lock_request(head)) {
int ret = nfs_wait_on_request(head);
if (ret < 0)
return ERR_PTR(ret);
}
if (head != req)
kref_get(&head->wb_kref);
return head;
}

/*
* nfs_unroll_locks - unlock all newly locked reqs and wait on @req
* @head: head request of page group, must be holding head lock
Expand Down Expand Up @@ -186,21 +205,24 @@ nfs_page_group_lock_subreq(struct nfs_page *head, struct nfs_page *subreq)
* @head: head request of page group
*
* This is a helper function for nfs_lock_and_join_requests which
* must be called with the head request and page group both locked.
* On error, it returns with the page group unlocked.
* must be called with the head request locked.
*/
int nfs_page_group_lock_subrequests(struct nfs_page *head)
{
struct nfs_page *subreq;
int ret;

ret = nfs_page_group_lock(head);
if (ret < 0)
return ret;
/* lock each request in the page group */
for (subreq = head->wb_this_page; subreq != head;
subreq = subreq->wb_this_page) {
ret = nfs_page_group_lock_subreq(head, subreq);
if (ret < 0)
return ret;
}
nfs_page_group_unlock(head);
return 0;
}

Expand Down
164 changes: 98 additions & 66 deletions fs/nfs/write.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -149,6 +149,31 @@ static void nfs_io_completion_put(struct nfs_io_completion *ioc)
kref_put(&ioc->refcount, nfs_io_completion_release);
}

static void
nfs_page_set_inode_ref(struct nfs_page *req, struct inode *inode)
{
if (!test_and_set_bit(PG_INODE_REF, &req->wb_flags)) {
kref_get(&req->wb_kref);
atomic_long_inc(&NFS_I(inode)->nrequests);
}
}

static int
nfs_cancel_remove_inode(struct nfs_page *req, struct inode *inode)
{
int ret;

if (!test_bit(PG_REMOVE, &req->wb_flags))
return 0;
ret = nfs_page_group_lock(req);
if (ret)
return ret;
if (test_and_clear_bit(PG_REMOVE, &req->wb_flags))
nfs_page_set_inode_ref(req, inode);
nfs_page_group_unlock(req);
return 0;
}

static struct nfs_page *
nfs_page_private_request(struct page *page)
{
Expand Down Expand Up @@ -218,6 +243,36 @@ static struct nfs_page *nfs_page_find_head_request(struct page *page)
return req;
}

static struct nfs_page *nfs_find_and_lock_page_request(struct page *page)
{
struct inode *inode = page_file_mapping(page)->host;
struct nfs_page *req, *head;
int ret;

for (;;) {
req = nfs_page_find_head_request(page);
if (!req)
return req;
head = nfs_page_group_lock_head(req);
if (head != req)
nfs_release_request(req);
if (IS_ERR(head))
return head;
ret = nfs_cancel_remove_inode(head, inode);
if (ret < 0) {
nfs_unlock_and_release_request(head);
return ERR_PTR(ret);
}
/* Ensure that nobody removed the request before we locked it */
if (head == nfs_page_private_request(page))
break;
if (PageSwapCache(page))
break;
nfs_unlock_and_release_request(head);
}
return head;
}

/* Adjust the file length if we're writing beyond the end */
static void nfs_grow_file(struct page *page, unsigned int offset, unsigned int count)
{
Expand Down Expand Up @@ -436,65 +491,22 @@ nfs_destroy_unlinked_subrequests(struct nfs_page *destroy_list,
}

/*
* nfs_lock_and_join_requests - join all subreqs to the head req and return
* a locked reference, cancelling any pending
* operations for this page.
*
* @page - the page used to lookup the "page group" of nfs_page structures
* nfs_join_page_group - destroy subrequests of the head req
* @head: the page used to lookup the "page group" of nfs_page structures
* @inode: Inode to which the request belongs.
*
* This function joins all sub requests to the head request by first
* locking all requests in the group, cancelling any pending operations
* and finally updating the head request to cover the whole range covered by
* the (former) group. All subrequests are removed from any write or commit
* lists, unlinked from the group and destroyed.
*
* Returns a locked, referenced pointer to the head request - which after
* this call is guaranteed to be the only request associated with the page.
* Returns NULL if no requests are found for @page, or a ERR_PTR if an
* error was encountered.
*/
static struct nfs_page *
nfs_lock_and_join_requests(struct page *page)
static void
nfs_join_page_group(struct nfs_page *head, struct inode *inode)
{
struct inode *inode = page_file_mapping(page)->host;
struct nfs_page *head, *subreq;
struct nfs_page *subreq;
struct nfs_page *destroy_list = NULL;
unsigned int pgbase, off, bytes;
int ret;

try_again:
/*
* A reference is taken only on the head request which acts as a
* reference to the whole page group - the group will not be destroyed
* until the head reference is released.
*/
head = nfs_page_find_head_request(page);
if (!head)
return NULL;

/* lock the page head first in order to avoid an ABBA inefficiency */
if (!nfs_lock_request(head)) {
ret = nfs_wait_on_request(head);
nfs_release_request(head);
if (ret < 0)
return ERR_PTR(ret);
goto try_again;
}

/* Ensure that nobody removed the request before we locked it */
if (head != nfs_page_private_request(page) && !PageSwapCache(page)) {
nfs_unlock_and_release_request(head);
goto try_again;
}

ret = nfs_page_group_lock(head);
if (ret < 0)
goto release_request;

/* lock each request in the page group */
ret = nfs_page_group_lock_subrequests(head);
if (ret < 0)
goto release_request;

pgbase = head->wb_pgbase;
bytes = head->wb_bytes;
Expand Down Expand Up @@ -531,30 +543,50 @@ nfs_lock_and_join_requests(struct page *page)
head->wb_this_page = head;
}

/* Postpone destruction of this request */
if (test_and_clear_bit(PG_REMOVE, &head->wb_flags)) {
set_bit(PG_INODE_REF, &head->wb_flags);
kref_get(&head->wb_kref);
atomic_long_inc(&NFS_I(inode)->nrequests);
}
nfs_destroy_unlinked_subrequests(destroy_list, head, inode);
}

nfs_page_group_unlock(head);
/*
* nfs_lock_and_join_requests - join all subreqs to the head req
* @page: the page used to lookup the "page group" of nfs_page structures
*
* This function joins all sub requests to the head request by first
* locking all requests in the group, cancelling any pending operations
* and finally updating the head request to cover the whole range covered by
* the (former) group. All subrequests are removed from any write or commit
* lists, unlinked from the group and destroyed.
*
* Returns a locked, referenced pointer to the head request - which after
* this call is guaranteed to be the only request associated with the page.
* Returns NULL if no requests are found for @page, or a ERR_PTR if an
* error was encountered.
*/
static struct nfs_page *
nfs_lock_and_join_requests(struct page *page)
{
struct inode *inode = page_file_mapping(page)->host;
struct nfs_page *head;
int ret;

nfs_destroy_unlinked_subrequests(destroy_list, head, inode);
/*
* A reference is taken only on the head request which acts as a
* reference to the whole page group - the group will not be destroyed
* until the head reference is released.
*/
head = nfs_find_and_lock_page_request(page);
if (IS_ERR_OR_NULL(head))
return head;

/* Did we lose a race with nfs_inode_remove_request()? */
if (!(PagePrivate(page) || PageSwapCache(page))) {
/* lock each request in the page group */
ret = nfs_page_group_lock_subrequests(head);
if (ret < 0) {
nfs_unlock_and_release_request(head);
return NULL;
return ERR_PTR(ret);
}

/* still holds ref on head from nfs_page_find_head_request
* and still has lock on head from lock loop */
return head;
nfs_join_page_group(head, inode);

release_request:
nfs_unlock_and_release_request(head);
return ERR_PTR(ret);
return head;
}

static void nfs_write_error(struct nfs_page *req, int error)
Expand Down
1 change: 1 addition & 0 deletions include/linux/nfs_page.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -139,6 +139,7 @@ extern size_t nfs_generic_pg_test(struct nfs_pageio_descriptor *desc,
extern int nfs_wait_on_request(struct nfs_page *);
extern void nfs_unlock_request(struct nfs_page *req);
extern void nfs_unlock_and_release_request(struct nfs_page *);
extern struct nfs_page *nfs_page_group_lock_head(struct nfs_page *req);
extern int nfs_page_group_lock_subrequests(struct nfs_page *head);
extern int nfs_page_group_lock(struct nfs_page *);
extern void nfs_page_group_unlock(struct nfs_page *);
Expand Down

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