mm: Add set/end/wait functions for PG_private_2

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:
v7:
- Use compound_head() in all the functions to make them THP safe[6].

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@linux-foundation.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Tested-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Dave Wysochanski <dwysocha@redhat.com>
Tested-By: Marc Dionne <marc.dionne@auristor.com>
cc: Alexander Viro <viro@zeniv.linux.org.uk>
cc: Christoph Hellwig <hch@lst.de>
cc: linux-mm@kvack.org
cc: linux-cachefs@redhat.com
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: v9fs-developer@lists.sourceforge.net
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/r/1330473.1612974547@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/CAHk-=wjgA-74ddehziVk=XAEMTKswPu1Yw4uaro1R3ibs27ztw@mail.gmail.com/ [1]
Link: https://lore.kernel.org/r/20210216102659.GA27714@lst.de/ [2]
Link: https://lore.kernel.org/r/161340387944.1303470.7944159520278177652.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/161539528910.286939.1252328699383291173.stgit@warthog.procyon.org.uk # v4
Link: https://lore.kernel.org/r/20210321105309.GG3420@casper.infradead.org [3]
Link: https://lore.kernel.org/r/CAHk-=wh+2gbF7XEjYc=HV9w_2uVzVf7vs60BPz0gFA=+pUm3ww@mail.gmail.com/ [4]
Link: https://lore.kernel.org/r/CAHk-=wjSGsRj7xwhSMQ6dAQiz53xA39pOG+XA_WeTgwBBu4uqg@mail.gmail.com/ [5]
Link: https://lore.kernel.org/r/20210408145057.GN2531743@casper.infradead.org/ [6]
Link: https://lore.kernel.org/r/161653788200.2770958.9517755716374927208.stgit@warthog.procyon.org.uk/ # v5
Link: https://lore.kernel.org/r/161789066013.6155.9816857201817288382.stgit@warthog.procyon.org.uk/ # v6
This commit is contained in:
David Howells 2020-02-10 10:00:21 +00:00
parent 7ff5062079
commit 73e10ded33
2 changed files with 81 additions and 0 deletions

View File

@ -688,6 +688,26 @@ 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)
{
page = compound_head(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
*/

View File

@ -1432,6 +1432,67 @@ 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)
{
page = compound_head(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;
page = compound_head(page);
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