Add three functions to manipulate PG_private_2:
(*) set_page_private_2() - Set the flag and take an appropriate reference
on the flagged page.
(*) end_page_private_2() - Clear the flag, drop the reference and wake up
any waiters, somewhat analogously with end_page_writeback().
(*) wait_on_page_private_2() - Wait for the flag to be cleared.
Wrappers will need to be placed in the netfs lib header in the patch that
adds that.
[This implements a suggestion by Linus[1] to not mix the terminology of
PG_private_2 and PG_fscache in the mm core function]
Changes:
v5:
- Add set and end functions, calling the end function end rather than
unlock[3].
- Keep a ref on the page when PG_private_2 is set[4][5].
v4:
- Remove extern from the declaration[2].
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
cc: Christoph Hellwig <hch@xxxxxx>
cc: linux-mm@xxxxxxxxx
cc: linux-cachefs@xxxxxxxxxx
cc: linux-afs@xxxxxxxxxxxxxxxxxxx
cc: linux-nfs@xxxxxxxxxxxxxxx
cc: linux-cifs@xxxxxxxxxxxxxxx
cc: ceph-devel@xxxxxxxxxxxxxxx
cc: v9fs-developer@xxxxxxxxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/1330473.1612974547@xxxxxxxxxxxxxxxxxxxxxx/ # v1
Link: https://lore.kernel.org/r/CAHk-=wjgA-74ddehziVk=XAEMTKswPu1Yw4uaro1R3ibs27ztw@xxxxxxxxxxxxxx/ [1]
Link: https://lore.kernel.org/r/20210216102659.GA27714@xxxxxx/ [2]
Link: https://lore.kernel.org/r/161340387944.1303470.7944159520278177652.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v3
Link: https://lore.kernel.org/r/161539528910.286939.1252328699383291173.stgit@xxxxxxxxxxxxxxxxxxxxxx # v4
Link: https://lore.kernel.org/r/20210321105309.GG3420@xxxxxxxxxxxxxxxxxxxx [3]
Link: https://lore.kernel.org/r/CAHk-=wh+2gbF7XEjYc=HV9w_2uVzVf7vs60BPz0gFA=+pUm3ww@xxxxxxxxxxxxxx/ [4]
Link: https://lore.kernel.org/r/CAHk-=wjSGsRj7xwhSMQ6dAQiz53xA39pOG+XA_WeTgwBBu4uqg@xxxxxxxxxxxxxx/ [5]
---
include/linux/pagemap.h | 19 +++++++++++++++
mm/filemap.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 78 insertions(+)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 444155ae56c0..da5c38864037 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -689,6 +689,25 @@ 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/mm/filemap.c b/mm/filemap.c
index 43700480d897..788b71e8a72d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1432,6 +1432,65 @@ void unlock_page(struct page *page)
}
EXPORT_SYMBOL(unlock_page);
+/**
+ * end_page_private_2 - Clear PG_private_2 and release any waiters
+ * @page: The page
+ *
+ * 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 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(wait_on_page_private_2_killable);
+
/**
* end_page_writeback - end writeback against a page
* @page: the page
