From: Linus Torvalds <torvalds@linux-foundation.org>
To: Steven Whitehouse <swhiteho@redhat.com>
Cc: "Andreas Grünbacher" <andreas.gruenbacher@gmail.com>,
"Konstantin Khlebnikov" <khlebnikov@yandex-team.ru>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Linux-MM <linux-mm@kvack.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"Johannes Weiner" <hannes@cmpxchg.org>,
"cluster-devel@redhat.com" <cluster-devel@redhat.com>,
"Ronnie Sahlberg" <lsahlber@redhat.com>,
"Steve French" <sfrench@samba.org>,
"Andreas Gruenbacher" <agruenba@redhat.com>,
"Bob Peterson" <rpeterso@redhat.com>
Subject: Re: [PATCH] mm/filemap: do not allocate cache pages beyond end of file at read
Date: Wed, 27 Nov 2019 09:29:44 -0800 [thread overview]
Message-ID: <CAHk-=wh5yeAj47x5EAuec7NCgFyYV1VtB9A+nBq+bVP9HmeepQ@mail.gmail.com> (raw)
In-Reply-To: <cdd48a4d-42a4-dd15-2701-e08e26fef17f@redhat.com>
On Wed, Nov 27, 2019 at 7:42 AM Steven Whitehouse <swhiteho@redhat.com> wrote:
>
> I'll leave the finer details to Andreas here, since it is his patch, and
> hopefully we can figure out a good path forward.
As mentioned, I don't _hate_ that patch (ok, I seem to have typoed it
and said that I don't "gate" it ;), so if that's what you guys really
want to do, I'm ok with it. But..
I do think you already get the data with the current case, from the
"short read" thing. So just changing the current generic read function
to check against the size first:
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2021,9 +2021,9 @@ static ssize_t
generic_file_buffered_read(struct kiocb *iocb,
unsigned int prev_offset;
int error = 0;
- if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
+ if (unlikely(*ppos >= inode->i_size))
return 0;
- iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
+ iov_iter_truncate(iter, inode->i_size);
index = *ppos >> PAGE_SHIFT;
prev_index = ra->prev_pos >> PAGE_SHIFT;
and you're done. Nice and clean.
Then in gfs2 you just notice the short read, and check at that point.
Sure, you'll also cut read-ahead to the old size boundary, but does
anybody _seriously_ believe that read-ahead matters when you hit the
"some other node write more data, we're reading past the old end"
case? I don't think that's the case.
But I _can_ live with the patch that adds the extra "cached only" bit.
It just honestly feels pointless.
Linus
prev parent reply other threads:[~2019-11-27 17:30 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-28 9:59 [PATCH] mm/filemap: do not allocate cache pages beyond end of file at read Konstantin Khlebnikov
2019-10-28 12:39 ` Linus Torvalds
2019-10-28 12:42 ` Kirill A. Shutemov
2019-10-28 12:47 ` Linus Torvalds
2019-10-28 12:57 ` Kirill A. Shutemov
2019-10-29 14:25 ` Konstantin Khlebnikov
2019-10-29 16:52 ` Linus Torvalds
2019-10-30 6:50 ` Kirill A. Shutemov
2019-10-30 7:02 ` Linus Torvalds
2019-10-30 10:34 ` Steven Whitehouse
2019-10-30 10:54 ` Linus Torvalds
2019-10-31 11:40 ` Steven Whitehouse
2019-11-22 23:59 ` Andreas Grünbacher
2019-11-25 10:52 ` Steven Whitehouse
2019-11-25 17:05 ` Linus Torvalds
2019-11-27 15:41 ` Steven Whitehouse
2019-11-27 16:29 ` Andreas Gruenbacher
2019-11-27 17:29 ` Linus Torvalds [this message]
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