linux-kernel - Re: [PATCH v6 02/30] mm: Add set/end/wait functions for PG_private

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Date:   Thu, 08 Apr 2021 16:57:31 +0100
From:   David Howells <dhowells@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     dhowells@...hat.com, linux-fsdevel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@....de>, linux-mm@...ck.org,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...hat.com>,
        David Wysochanski <dwysocha@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 02/30] mm: Add set/end/wait functions for PG_private_2

Here's a partial change, but we still need to deal with the assumption that
page_has_private() makes that its output can be used to count the number of
refs held for PG_private *and* PG_private_2 - which isn't true for my code
here.

David
---
commit e7c28d83b84b972c3faa0dd86020548aa50eda75
Author: David Howells <dhowells@...hat.com>
Date:   Thu Apr 8 16:33:20 2021 +0100

    netfs: Fix PG_private_2 helper functions to consistently use compound_head()

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ef511364cc0c..63ca6430aef5 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -699,6 +699,7 @@ void page_endio(struct page *page, bool is_write, int err);
  */
 static inline void set_page_private_2(struct page *page)
 {
+	page = compound_head(page);
 	get_page(page);
 	SetPagePrivate2(page);
 }
diff --git a/mm/filemap.c b/mm/filemap.c
index 0ce93c8799ca..46e0321ba87a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1461,6 +1461,7 @@ EXPORT_SYMBOL(end_page_private_2);
  */
 void wait_on_page_private_2(struct page *page)
 {
+	page = compound_head(page);
 	while (PagePrivate2(page))
 		wait_on_page_bit(page, PG_private_2);
 }
@@ -1481,6 +1482,7 @@ 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)