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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <2213409.1677249075@warthog.procyon.org.uk>
References: <2213409.1677249075@warthog.procyon.org.uk> <2134430.1677240738@warthog.procyon.org.uk> <2009825.1677229488@warthog.procyon.org.uk> <CAHk-=whAAOVBrzwb2uMjCmdRrtudGesYj0tuqdUgi8X_gbw1jw@mail.gmail.com> <20230220135225.91b0f28344c01d5306c31230@linux-foundation.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        Steve French <stfrench@microsoft.com>
Cc:     dhowells@redhat.com, Vishal Moola <vishal.moola@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jan Kara <jack@suse.cz>, Paulo Alcantara <pc@cjr.nz>,
        Matthew Wilcox <willy@infradead.org>,
        Huang Ying <ying.huang@intel.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Xin Hao <xhao@linux.alibaba.com>, linux-mm@kvack.org,
        mm-commits@vger.kernel.org, linux-cifs@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [RFC][PATCH] cifs: Improve use of filemap_get_folios_tag()
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Date:   Fri, 24 Feb 2023 15:13:06 +0000
Message-ID: <2244151.1677251586@warthog.procyon.org.uk>
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[This additional to the "cifs: Fix cifs_writepages_region()" patch that I
posted]

The inefficiency derived from filemap_get_folios_tag() get a batch of
contiguous folios in Vishal's change to afs that got copied into cifs can
be reduced by skipping over those folios that have been passed by the star=
t
position rather than going through the process of locking, checking and
trying to write them.

A similar change would need to be made in afs, in addition to fixing the b=
ugs
there.

There's also a fix in cifs_write_back_from_locked_folio() where it doesn't
return the amount of data dispatched to the server as ->async_writev() jus=
t
returns 0 on success.

Signed-off-by: David Howells <dhowells@redhat.com>
---
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index ebfcaae8c437..bae1a9709e32 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2839,6 +2839,7 @@ static ssize_t cifs_write_back_from_locked_folio(str=
uct address_space *mapping,
 	free_xid(xid);
 	if (rc =3D=3D 0) {
 		wbc->nr_to_write =3D count;
+		rc =3D len;
 	} else if (is_retryable_error(rc)) {
 		cifs_pages_write_redirty(inode, start, len);
 	} else {
@@ -2873,6 +2874,13 @@ static int cifs_writepages_region(struct address_sp=
ace *mapping,
 		for (int i =3D 0; i < nr; i++) {
 			ssize_t ret;
 			struct folio *folio =3D fbatch.folios[i];
+			unsigned long long fstart;
+
+			fstart =3D folio_pos(folio); /* May go backwards with THPs */
+			if (fstart < start &&
+			    folio_size(folio) <=3D start - fstart)
+				continue;
+			start =3D fstart;
 =

 redo_folio:
 			start =3D folio_pos(folio); /* May regress with THPs */