nfs: handle multiple reqs in nfs_page_async_flush

Change nfs_find_and_lock_request so nfs_page_async_flush can handle multiple
requests in a page. There is only one request for a page the first time
nfs_page_async_flush is called, but if a write or commit fails, async_flush
is called again and there may be multiple requests associated with the page.
The solution is to merge all the requests in a page group into a single
request before calling nfs_pageio_add_request.

Rename nfs_find_and_lock_request to nfs_lock_and_join_requests and
change it to first lock all requests for the page, then cancel and merge
all subrequests into the head request.

Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
This commit is contained in:
Weston Andros Adamson 2014-07-11 10:20:48 -04:00 committed by Trond Myklebust
parent 84d3a9a913
commit d458138353
3 changed files with 240 additions and 30 deletions

View File

@ -244,6 +244,7 @@ void nfs_pgio_data_release(struct nfs_pgio_data *);
int nfs_generic_pgio(struct nfs_pageio_descriptor *, struct nfs_pgio_header *);
int nfs_initiate_pgio(struct rpc_clnt *, struct nfs_pgio_data *,
const struct rpc_call_ops *, int, int);
void nfs_free_request(struct nfs_page *req);
static inline void nfs_iocounter_init(struct nfs_io_counter *c)
{

View File

@ -29,8 +29,6 @@
static struct kmem_cache *nfs_page_cachep;
static const struct rpc_call_ops nfs_pgio_common_ops;
static void nfs_free_request(struct nfs_page *);
static bool nfs_pgarray_set(struct nfs_page_array *p, unsigned int pagecount)
{
p->npages = pagecount;
@ -406,7 +404,7 @@ static void nfs_clear_request(struct nfs_page *req)
*
* Note: Should never be called with the spinlock held!
*/
static void nfs_free_request(struct nfs_page *req)
void nfs_free_request(struct nfs_page *req)
{
WARN_ON_ONCE(req->wb_this_page != req);

View File

@ -46,6 +46,7 @@ static const struct rpc_call_ops nfs_commit_ops;
static const struct nfs_pgio_completion_ops nfs_async_write_completion_ops;
static const struct nfs_commit_completion_ops nfs_commit_completion_ops;
static const struct nfs_rw_ops nfs_rw_write_ops;
static void nfs_clear_request_commit(struct nfs_page *req);
static struct kmem_cache *nfs_wdata_cachep;
static mempool_t *nfs_wdata_mempool;
@ -289,36 +290,246 @@ static void nfs_end_page_writeback(struct nfs_page *req)
clear_bdi_congested(&nfss->backing_dev_info, BLK_RW_ASYNC);
}
static struct nfs_page *nfs_find_and_lock_request(struct page *page, bool nonblock)
/* nfs_page_group_clear_bits
* @req - an nfs request
* clears all page group related bits from @req
*/
static void
nfs_page_group_clear_bits(struct nfs_page *req)
{
struct inode *inode = page_file_mapping(page)->host;
struct nfs_page *req;
clear_bit(PG_TEARDOWN, &req->wb_flags);
clear_bit(PG_UNLOCKPAGE, &req->wb_flags);
clear_bit(PG_UPTODATE, &req->wb_flags);
clear_bit(PG_WB_END, &req->wb_flags);
clear_bit(PG_REMOVE, &req->wb_flags);
}
/*
* nfs_unroll_locks_and_wait - unlock all newly locked reqs and wait on @req
*
* this is a helper function for nfs_lock_and_join_requests
*
* @inode - inode associated with request page group, must be holding inode lock
* @head - head request of page group, must be holding head lock
* @req - request that couldn't lock and needs to wait on the req bit lock
* @nonblock - if true, don't actually wait
*
* NOTE: this must be called holding page_group bit lock and inode spin lock
* and BOTH will be released before returning.
*
* returns 0 on success, < 0 on error.
*/
static int
nfs_unroll_locks_and_wait(struct inode *inode, struct nfs_page *head,
struct nfs_page *req, bool nonblock)
__releases(&inode->i_lock)
{
struct nfs_page *tmp;
int ret;
spin_lock(&inode->i_lock);
for (;;) {
req = nfs_page_find_head_request_locked(NFS_I(inode), page);
if (req == NULL)
break;
if (nfs_lock_request(req))
break;
/* Note: If we hold the page lock, as is the case in nfs_writepage,
* then the call to nfs_lock_request() will always
* succeed provided that someone hasn't already marked the
* request as dirty (in which case we don't care).
*/
spin_unlock(&inode->i_lock);
if (!nonblock)
ret = nfs_wait_on_request(req);
else
ret = -EAGAIN;
nfs_release_request(req);
if (ret != 0)
return ERR_PTR(ret);
spin_lock(&inode->i_lock);
}
/* relinquish all the locks successfully grabbed this run */
for (tmp = head ; tmp != req; tmp = tmp->wb_this_page)
nfs_unlock_request(tmp);
WARN_ON_ONCE(test_bit(PG_TEARDOWN, &req->wb_flags));
/* grab a ref on the request that will be waited on */
kref_get(&req->wb_kref);
nfs_page_group_unlock(head);
spin_unlock(&inode->i_lock);
return req;
/* release ref from nfs_page_find_head_request_locked */
nfs_release_request(head);
if (!nonblock)
ret = nfs_wait_on_request(req);
else
ret = -EAGAIN;
nfs_release_request(req);
return ret;
}
/*
* nfs_destroy_unlinked_subrequests - destroy recently unlinked subrequests
*
* @destroy_list - request list (using wb_this_page) terminated by @old_head
* @old_head - the old head of the list
*
* All subrequests must be locked and removed from all lists, so at this point
* they are only "active" in this function, and possibly in nfs_wait_on_request
* with a reference held by some other context.
*/
static void
nfs_destroy_unlinked_subrequests(struct nfs_page *destroy_list,
struct nfs_page *old_head)
{
while (destroy_list) {
struct nfs_page *subreq = destroy_list;
destroy_list = (subreq->wb_this_page == old_head) ?
NULL : subreq->wb_this_page;
WARN_ON_ONCE(old_head != subreq->wb_head);
/* make sure old group is not used */
subreq->wb_head = subreq;
subreq->wb_this_page = subreq;
nfs_clear_request_commit(subreq);
/* subreq is now totally disconnected from page group or any
* write / commit lists. last chance to wake any waiters */
nfs_unlock_request(subreq);
if (!test_bit(PG_TEARDOWN, &subreq->wb_flags)) {
/* release ref on old head request */
nfs_release_request(old_head);
nfs_page_group_clear_bits(subreq);
/* release the PG_INODE_REF reference */
if (test_and_clear_bit(PG_INODE_REF, &subreq->wb_flags))
nfs_release_request(subreq);
else
WARN_ON_ONCE(1);
} else {
WARN_ON_ONCE(test_bit(PG_CLEAN, &subreq->wb_flags));
/* zombie requests have already released the last
* reference and were waiting on the rest of the
* group to complete. Since it's no longer part of a
* group, simply free the request */
nfs_page_group_clear_bits(subreq);
nfs_free_request(subreq);
}
}
}
/*
* 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
* @nonblock - if true, don't block waiting for request locks
*
* 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, bool nonblock)
{
struct inode *inode = page_file_mapping(page)->host;
struct nfs_page *head, *subreq;
struct nfs_page *destroy_list = NULL;
unsigned int total_bytes;
int ret;
try_again:
total_bytes = 0;
WARN_ON_ONCE(destroy_list);
spin_lock(&inode->i_lock);
/*
* 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_locked(NFS_I(inode), page);
if (!head) {
spin_unlock(&inode->i_lock);
return NULL;
}
/* lock each request in the page group */
nfs_page_group_lock(head);
subreq = head;
do {
/*
* Subrequests are always contiguous, non overlapping
* and in order. If not, it's a programming error.
*/
WARN_ON_ONCE(subreq->wb_offset !=
(head->wb_offset + total_bytes));
/* keep track of how many bytes this group covers */
total_bytes += subreq->wb_bytes;
if (!nfs_lock_request(subreq)) {
/* releases page group bit lock and
* inode spin lock and all references */
ret = nfs_unroll_locks_and_wait(inode, head,
subreq, nonblock);
if (ret == 0)
goto try_again;
return ERR_PTR(ret);
}
subreq = subreq->wb_this_page;
} while (subreq != head);
/* Now that all requests are locked, make sure they aren't on any list.
* Commit list removal accounting is done after locks are dropped */
subreq = head;
do {
nfs_list_remove_request(subreq);
subreq = subreq->wb_this_page;
} while (subreq != head);
/* unlink subrequests from head, destroy them later */
if (head->wb_this_page != head) {
/* destroy list will be terminated by head */
destroy_list = head->wb_this_page;
head->wb_this_page = head;
/* change head request to cover whole range that
* the former page group covered */
head->wb_bytes = total_bytes;
}
/*
* prepare head request to be added to new pgio descriptor
*/
nfs_page_group_clear_bits(head);
/*
* some part of the group was still on the inode list - otherwise
* the group wouldn't be involved in async write.
* grab a reference for the head request, iff it needs one.
*/
if (!test_and_set_bit(PG_INODE_REF, &head->wb_flags))
kref_get(&head->wb_kref);
nfs_page_group_unlock(head);
/* drop lock to clear_request_commit the head req and clean up
* requests on destroy list */
spin_unlock(&inode->i_lock);
nfs_destroy_unlinked_subrequests(destroy_list, head);
/* clean up commit list state */
nfs_clear_request_commit(head);
/* still holds ref on head from nfs_page_find_head_request_locked
* and still has lock on head from lock loop */
return head;
}
/*
@ -331,7 +542,7 @@ static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio,
struct nfs_page *req;
int ret = 0;
req = nfs_find_and_lock_request(page, nonblock);
req = nfs_lock_and_join_requests(page, nonblock);
if (!req)
goto out;
ret = PTR_ERR(req);