[PATCH v4 02/28] mm: Add an unlock function for PG_private_2/PG_fscache
David Howells
dhowells at redhat.com
Tue Mar 23 13:17:20 GMT 2021
David Howells <dhowells at redhat.com> wrote:
> Matthew Wilcox <willy at infradead.org> wrote:
>
> > That also brings up that there is no set_page_private_2(). I think
> > that's OK -- you only set PageFsCache() immediately after reading the
> > page from the server. But I feel this "unlock_page_private_2" is actually
> > "clear_page_private_2" -- ie it's equivalent to writeback, not to lock.
>
> How about I do the following:
>
> (1) Add set_page_private_2() or mark_page_private_2() to set the PG_fscache_2
> bit. It could take a ref on the page here.
>
> (2) Rename unlock_page_private_2() to end_page_private_2(). It could drop
> the ref on the page here, but that then means I can't use
> pagevec_release().
>
> (3) Add wait_on_page_private_2() an analogue of wait_on_page_writeback()
> rather than wait_on_page_locked().
>
> (4) Provide fscache synonyms of the above.
Perhaps something like the attached changes (they'll need merging back into
the other patches).
David
---
include/linux/pagemap.h | 21 +++++++++++++++++-
include/linux/netfs.h | 54 ++++++++++++++++++++++++++++++++++++------------
fs/afs/write.c | 5 ++--
fs/netfs/read_helper.c | 17 +++++----------
mm/filemap.c | 49 +++++++++++++++++++++++++++++++++++++++----
mm/page-writeback.c | 25 ++++++++++++++++++++++
6 files changed, 139 insertions(+), 32 deletions(-)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index bf05e99ce588..5c14a9365aae 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -591,7 +591,6 @@ extern int __lock_page_async(struct page *page, struct wait_page_queue *wait);
extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags);
extern void unlock_page(struct page *page);
-void unlock_page_private_2(struct page *page);
/*
* Return true if the page was successfully locked
@@ -684,11 +683,31 @@ static inline int wait_on_page_locked_killable(struct page *page)
int put_and_wait_on_page_locked(struct page *page, int state);
void wait_on_page_writeback(struct page *page);
+int wait_on_page_writeback_killable(struct page *page);
extern void end_page_writeback(struct page *page);
void wait_for_stable_page(struct page *page);
void page_endio(struct page *page, bool is_write, int err);
+/**
+ * set_page_private_2 - Set PG_private_2 on a page and take a ref
+ * @page: The page.
+ *
+ * Set the PG_private_2 flag on a page and take the reference needed for the VM
+ * to handle its lifetime correctly. This sets the flag and takes the
+ * reference unconditionally, so care must be taken not to set the flag again
+ * if it's already set.
+ */
+static inline void set_page_private_2(struct page *page)
+{
+ get_page(page);
+ SetPagePrivate2(page);
+}
+
+void end_page_private_2(struct page *page);
+void wait_on_page_private_2(struct page *page);
+int wait_on_page_private_2_killable(struct page *page);
+
/*
* Add an arbitrary waiter to a page's wait queue
*/
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 9d3fbed4e30a..2299e7662ff0 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -29,32 +29,60 @@
#define TestClearPageFsCache(page) TestClearPagePrivate2((page))
/**
- * unlock_page_fscache - Unlock a page that's locked with PG_fscache
- * @page: The page
+ * set_page_fscache - Set PG_fscache on a page and take a ref
+ * @page: The page.
*
- * Unlocks a page that's locked with PG_fscache and wakes up sleepers in
- * wait_on_page_fscache(). This page bit is used by the netfs helpers when a
- * netfs page is being written to a local disk cache, thereby allowing writes
- * to the cache for the same page to be serialised.
+ * Set the PG_fscache (PG_private_2) flag on a page and take the reference
+ * needed for the VM to handle its lifetime correctly. This sets the flag and
+ * takes the reference unconditionally, so care must be taken not to set the
+ * flag again if it's already set.
*/
-static inline void unlock_page_fscache(struct page *page)
+static inline void set_page_fscache(struct page *page)
{
- unlock_page_private_2(page);
+ set_page_private_2(page);
}
/**
- * wait_on_page_fscache - Wait for PG_fscache to be cleared on a page
+ * end_page_fscache - Clear PG_fscache and release any waiters
* @page: The page
*
- * Wait for the PG_fscache (PG_private_2) page bit to be removed from a page.
- * This is, for example, used to handle a netfs page being written to a local
+ * Clear the PG_fscache (PG_private_2) bit on a page and wake up any sleepers
+ * waiting for this. The page ref held for PG_private_2 being set is released.
+ *
+ * This is, for example, used when a netfs page is being written to a local
* disk cache, thereby allowing writes to the cache for the same page to be
* serialised.
*/
+static inline void end_page_fscache(struct page *page)
+{
+ end_page_private_2(page);
+}
+
+/**
+ * wait_on_page_fscache - Wait for PG_fscache to be cleared on a page
+ * @page: The page to wait on
+ *
+ * Wait for PG_fscache (aka PG_private_2) to be cleared on a page.
+ */
static inline void wait_on_page_fscache(struct page *page)
{
- if (PageFsCache(page))
- wait_on_page_bit(compound_head(page), PG_fscache);
+ wait_on_page_private_2(page);
+}
+
+/**
+ * wait_on_page_fscache_killable - Wait for PG_fscache to be cleared on a page
+ * @page: The page to wait on
+ *
+ * Wait for PG_fscache (aka PG_private_2) to be cleared on a page or until a
+ * fatal signal is received by the calling task.
+ *
+ * Return:
+ * - 0 if successful.
+ * - -EINTR if a fatal signal was encountered.
+ */
+static inline int wait_on_page_fscache_killable(struct page *page)
+{
+ return wait_on_page_private_2_killable(page);
}
enum netfs_read_source {
diff --git a/fs/afs/write.c b/fs/afs/write.c
index b2e03de09c24..9f82e2bb463e 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -846,7 +846,7 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
*/
#ifdef CONFIG_AFS_FSCACHE
if (PageFsCache(page) &&
- wait_on_page_bit_killable(page, PG_fscache) < 0)
+ wait_on_page_fscache_killable(page) < 0)
return VM_FAULT_RETRY;
#endif
@@ -861,7 +861,8 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
* details the portion of the page we need to write back and we might
* need to redirty the page if there's a problem.
*/
- wait_on_page_writeback(page);
+ if (wait_on_page_writeback_killable(page) < 0)
+ return VM_FAULT_RETRY | VM_FAULT_LOCKED;
priv = afs_page_dirty(page, 0, thp_size(page));
priv = afs_page_dirty_mmapped(priv);
diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 56e90e0388f2..2b23584499b2 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -239,13 +239,10 @@ static void netfs_rreq_unmark_after_write(struct netfs_read_request *rreq,
bool was_async)
{
struct netfs_read_subrequest *subreq;
- struct pagevec pvec;
struct page *page;
pgoff_t unlocked = 0;
bool have_unlocked = false;
- pagevec_init(&pvec);
-
rcu_read_lock();
list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
@@ -258,9 +255,7 @@ static void netfs_rreq_unmark_after_write(struct netfs_read_request *rreq,
if (have_unlocked && page->index <= unlocked)
continue;
unlocked = page->index;
- unlock_page_fscache(page);
- if (pagevec_add(&pvec, page) == 0)
- pagevec_release(&pvec);
+ end_page_fscache(page);
have_unlocked = true;
}
}
@@ -419,10 +414,8 @@ static void netfs_rreq_unlock(struct netfs_read_request *rreq)
pg_failed = true;
break;
}
- if (test_bit(NETFS_SREQ_WRITE_TO_CACHE, &subreq->flags)) {
- get_page(page);
- SetPageFsCache(page);
- }
+ if (test_bit(NETFS_SREQ_WRITE_TO_CACHE, &subreq->flags))
+ set_page_fscache(page);
pg_failed |= subreq_failed;
if (pgend < iopos + subreq->len)
break;
@@ -1167,7 +1160,9 @@ int netfs_write_begin(struct file *file, struct address_space *mapping,
goto error;
have_page:
- wait_on_page_fscache(page);
+ ret = wait_on_page_fscache_killable(page);
+ if (ret < 0)
+ goto error;
have_page_no_wait:
if (netfs_priv)
ops->cleanup(netfs_priv, mapping);
diff --git a/mm/filemap.c b/mm/filemap.c
index 925964b67583..788b71e8a72d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1433,24 +1433,63 @@ void unlock_page(struct page *page)
EXPORT_SYMBOL(unlock_page);
/**
- * unlock_page_private_2 - Unlock a page that's locked with PG_private_2
+ * end_page_private_2 - Clear PG_private_2 and release any waiters
* @page: The page
*
- * Unlocks a page that's locked with PG_private_2 and wakes up sleepers in
- * wait_on_page_private_2().
+ * Clear the PG_private_2 bit on a page and wake up any sleepers waiting for
+ * this. The page ref held for PG_private_2 being set is released.
*
* This is, for example, used when a netfs page is being written to a local
* disk cache, thereby allowing writes to the cache for the same page to be
* serialised.
*/
-void unlock_page_private_2(struct page *page)
+void end_page_private_2(struct page *page)
{
page = compound_head(page);
VM_BUG_ON_PAGE(!PagePrivate2(page), page);
clear_bit_unlock(PG_private_2, &page->flags);
wake_up_page_bit(page, PG_private_2);
+ put_page(page);
+}
+EXPORT_SYMBOL(end_page_private_2);
+
+/**
+ * wait_on_page_private_2 - Wait for PG_private_2 to be cleared on a page
+ * @page: The page to wait on
+ *
+ * Wait for PG_private_2 (aka PG_fscache) to be cleared on a page.
+ */
+void wait_on_page_private_2(struct page *page)
+{
+ while (PagePrivate2(page))
+ wait_on_page_bit(page, PG_private_2);
+}
+EXPORT_SYMBOL(wait_on_page_private_2);
+
+/**
+ * wait_on_page_private_2_killable - Wait for PG_private_2 to be cleared on a page
+ * @page: The page to wait on
+ *
+ * Wait for PG_private_2 (aka PG_fscache) to be cleared on a page or until a
+ * fatal signal is received by the calling task.
+ *
+ * Return:
+ * - 0 if successful.
+ * - -EINTR if a fatal signal was encountered.
+ */
+int wait_on_page_private_2_killable(struct page *page)
+{
+ int ret = 0;
+
+ while (PagePrivate2(page)) {
+ ret = wait_on_page_bit_killable(page, PG_private_2);
+ if (ret < 0)
+ break;
+ }
+
+ return ret;
}
-EXPORT_SYMBOL(unlock_page_private_2);
+EXPORT_SYMBOL(wait_on_page_private_2_killable);
/**
* end_page_writeback - end writeback against a page
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index eb34d204d4ee..b8bad275f94b 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2833,6 +2833,31 @@ void wait_on_page_writeback(struct page *page)
}
EXPORT_SYMBOL_GPL(wait_on_page_writeback);
+/**
+ * Wait for a page to complete writeback
+ * @page: The page to wait on
+ *
+ * Wait for the writeback status of a page to clear or a fatal signal to occur.
+ *
+ * Return:
+ * - 0 on success.
+ * - -EINTR if a fatal signal was encountered.
+ */
+int wait_on_page_writeback_killable(struct page *page)
+{
+ int ret = 0;
+
+ while (PageWriteback(page)) {
+ trace_wait_on_page_writeback(page, page_mapping(page));
+ ret = wait_on_page_bit_killable(page, PG_writeback);
+ if (ret < 0)
+ break;
+ }
+
+ return ret;
+}
+EXPORT_SYMBOL(wait_on_page_writeback_killable);
+
/**
* wait_for_stable_page() - wait for writeback to finish, if necessary.
* @page: The page to wait on.
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