From: Michal Hocko <mhocko@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: William Kucharski <william.kucharski@oracle.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org,
Dave Hansen <dave.hansen@linux.intel.com>,
Song Liu <songliubraving@fb.com>,
Bob Kasten <robert.a.kasten@intel.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Chad Mynhier <chad.mynhier@oracle.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Johannes Weiner <jweiner@fb.com>
Subject: Re: [PATCH v5 2/2] mm,thp: Add experimental config option RO_EXEC_FILEMAP_HUGE_FAULT_THP
Date: Tue, 3 Sep 2019 21:15:28 +0200 [thread overview]
Message-ID: <20190903191528.GC14028@dhcp22.suse.cz> (raw)
In-Reply-To: <20190903151015.GF29434@bombadil.infradead.org>
On Tue 03-09-19 08:10:15, Matthew Wilcox wrote:
> On Tue, Sep 03, 2019 at 02:51:50PM +0200, Michal Hocko wrote:
> > On Tue 03-09-19 05:22:08, Matthew Wilcox wrote:
> > > On Tue, Sep 03, 2019 at 02:14:24PM +0200, Michal Hocko wrote:
> > > > On Mon 02-09-19 03:23:41, William Kucharski wrote:
> > > > > Add filemap_huge_fault() to attempt to satisfy page
> > > > > faults on memory-mapped read-only text pages using THP when possible.
> > > >
> > > > This deserves much more description of how the thing is implemented and
> > > > expected to work. For one thing it is not really clear to me why you
> > > > need CONFIG_RO_EXEC_FILEMAP_HUGE_FAULT_THP at all. You need a support
> > > > from the filesystem anyway. So who is going to enable/disable this
> > > > config?
> > >
> > > There are definitely situations in which enabling this code will crash
> > > the kernel. But we want to get filesystems to a point where they can
> > > start working on their support for large pages. So our workaround is
> > > to try to get the core pieces merged under a CONFIG_I_KNOW_WHAT_IM_DOING
> > > flag and let people play with it. Then continue to work on the core
> > > to eliminate those places that are broken.
> >
> > I am not sure I understand. Each fs has to opt in to the feature
> > anyway. If it doesn't then there should be no risk of regression, right?
> > I do not expect any fs would rush an implementation in while not being
> > sure about the correctness. So how exactly does a config option help
> > here.
>
> Filesystems won't see large pages unless they've opted into them.
> But there's a huge amount of page-cache work that needs to get done
> before this can be enabled by default. For example, truncate() won't
> work properly.
>
> Rather than try to do all the page cache work upfront, then wait for the
> filesystems to catch up, we want to get some basics merged. Since we've
> been talking about this for so long without any movement in the kernel
> towards actual support, this felt like a good way to go.
>
> We could, of course, develop the entire thing out of tree, but that's
> likely to lead to pain and anguish.
Then I would suggest mentioning all this in the changelog so that the
overall intention is clear. It is also up to you fs developers to find a
consensus on how to move forward. I have brought that up mostly because
I really hate seeing new config options added due to shortage of
confidence in the code. That really smells like working around standard
code quality inclusion process.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-09-03 19:15 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-02 9:23 [PATCH v5 0/2] mm,thp: Add filemap_huge_fault() for THP William Kucharski
2019-09-02 9:23 ` [PATCH v5 1/2] mm: Allow the page cache to allocate large pages William Kucharski
2019-09-03 11:57 ` Michal Hocko
2019-09-03 12:11 ` Matthew Wilcox
2019-09-03 12:19 ` Michal Hocko
2019-09-03 16:28 ` Matthew Wilcox
2019-09-03 19:18 ` Michal Hocko
2019-09-04 3:30 ` William Kucharski
2019-09-04 8:28 ` Michal Hocko
2019-09-02 9:23 ` [PATCH v5 2/2] mm,thp: Add experimental config option RO_EXEC_FILEMAP_HUGE_FAULT_THP William Kucharski
2019-09-03 12:14 ` Michal Hocko
2019-09-03 12:22 ` Matthew Wilcox
2019-09-03 12:51 ` Michal Hocko
2019-09-03 15:10 ` Matthew Wilcox
2019-09-03 19:15 ` Michal Hocko [this message]
2019-09-04 3:23 ` William Kucharski
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190903191528.GC14028@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=chad.mynhier@oracle.com \
--cc=dave.hansen@linux.intel.com \
--cc=jweiner@fb.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mike.kravetz@oracle.com \
--cc=robert.a.kasten@intel.com \
--cc=songliubraving@fb.com \
--cc=william.kucharski@oracle.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).