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 1/2] mm: Allow the page cache to allocate large pages
Date: Tue, 3 Sep 2019 21:18:19 +0200 [thread overview]
Message-ID: <20190903191819.GD14028@dhcp22.suse.cz> (raw)
In-Reply-To: <20190903162831.GI29434@bombadil.infradead.org>
On Tue 03-09-19 09:28:31, Matthew Wilcox wrote:
> On Tue, Sep 03, 2019 at 02:19:52PM +0200, Michal Hocko wrote:
> > On Tue 03-09-19 05:11:55, Matthew Wilcox wrote:
> > > On Tue, Sep 03, 2019 at 01:57:48PM +0200, Michal Hocko wrote:
> > > > On Mon 02-09-19 03:23:40, William Kucharski wrote:
> > > > > Add an 'order' argument to __page_cache_alloc() and
> > > > > do_read_cache_page(). Ensure the allocated pages are compound pages.
> > > >
> > > > Why do we need to touch all the existing callers and change them to use
> > > > order 0 when none is actually converted to a different order? This just
> > > > seem to add a lot of code churn without a good reason. If anything I
> > > > would simply add __page_cache_alloc_order and make __page_cache_alloc
> > > > call it with order 0 argument.
> > >
> > > Patch 2/2 uses a non-zero order.
> >
> > It is a new caller and it can use a new function right?
> >
> > > I agree it's a lot of churn without
> > > good reason; that's why I tried to add GFP_ORDER flags a few months ago.
> > > Unfortunately, you didn't like that approach either.
> >
> > Is there any future plan that all/most __page_cache_alloc will get a
> > non-zero order argument?
>
> I'm not sure about "most". It will certainly become more common, as
> far as I can tell.
I would personally still go with __page_cache_alloc_order way, but this
is up to you and other fs people what suits best. I was just surprised
to see a lot of code churn when it was not really used in the second
patch. That's why I brought it up.
> > > > Also is it so much to ask callers to provide __GFP_COMP explicitly?
> > >
> > > Yes, it's an unreasonable burden on the callers.
> >
> > Care to exaplain why? __GFP_COMP tends to be used in the kernel quite
> > extensively.
>
> Most of the places which call this function get their gfp_t from
> mapping->gfp_mask. If we only want to allocate a single page, we
> must not set __GFP_COMP. If we want to allocate a large page, we must
> set __GFP_COMP. Rather than require individual filesystems to concern
> themselves with this wart of the GFP interface, we can solve it in the
> page cache.
Fair enough.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-09-03 19:18 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 [this message]
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
2019-09-04 3:23 ` William Kucharski
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