Re: [External] Re: [PATCH v10 03/11] mm/hugetlb: Free the vmemmap pages associated with each HugeTLB page

From: Muchun Song <songmuchun@bytedance.com>
To: Oscar Salvador <osalvador@suse.de>
Cc: Jonathan Corbet <corbet@lwn.net>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	dave.hansen@linux.intel.com, luto@kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	viro@zeniv.linux.org.uk,
	Andrew Morton <akpm@linux-foundation.org>,
	paulmck@kernel.org, mchehab+huawei@kernel.org,
	pawan.kumar.gupta@linux.intel.com,
	Randy Dunlap <rdunlap@infradead.org>,
	oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de,
	Mina Almasry <almasrymina@google.com>,
	David Rientjes <rientjes@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	Michal Hocko <mhocko@suse.com>,
	"Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
	David Hildenbrand <david@redhat.com>,
	naoya.horiguchi@nec.com,
	Xiongchun duan <duanxiongchun@bytedance.com>,
	linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [External] Re: [PATCH v10 03/11] mm/hugetlb: Free the vmemmap pages associated with each HugeTLB page
Date: Tue, 22 Dec 2020 10:49:35 +0800	[thread overview]
Message-ID: <CAMZfGtVsJz-vt-vsgGBAxGOKdibCAxBsnjEpupKX_=Tw9rZZ3A@mail.gmail.com> (raw)
In-Reply-To: <20201221180019.GA2884@localhost.localdomain>

On Tue, Dec 22, 2020 at 2:00 AM Oscar Salvador <osalvador@suse.de> wrote:
>
> On Mon, Dec 21, 2020 at 11:52:30PM +0800, Muchun Song wrote:
> > On Mon, Dec 21, 2020 at 9:44 PM Oscar Salvador <osalvador@suse.de> wrote:
> > >
> > > On Mon, Dec 21, 2020 at 07:25:15PM +0800, Muchun Song wrote:
> > >
> > > > Should we add a BUG_ON in vmemmap_remap_free() for now?
> > > >
> > > >         BUG_ON(reuse != start + PAGE_SIZE);
> > >
> > > I do not think we have to, plus we would be BUG_ing for some specific use
> > > case in "generic" function.
> >
> > The vmemmap_remap_range() walks page table range [start, end),
> > if reuse is equal to (start + PAGE_SIZE), the range can adjust to
> > [start - PAGE_SIZE, end). But if not, we need some work to
> > implement the "generic" function.
> >
> >   - adjust range to [min(start, reuse), end) and call
> >     vmemmap_remap_rangeand which skip the hole
> >     which is [reuse + PAGE_SIZE, start) or [end, reuse).
> >   - call vmemmap_remap_range(reuse, reuse + PAGE_SIZE)
> >     to get the reuse page.Then, call vmemmap_remap_range(start, end)
> >     again to remap.
> >
> > Which one do you prefer?
>
> I would not overcomplicate things at this stage.
> Just follow my sugestion and add a BUG_ON as you said, that might be the
> easier way now.
> We can overthink this in the future when some other usecases come
> around, right?

You are right. Will do this. Thanks for your suggestions.

>
> Thanks
>
>
> --
> Oscar Salvador
> SUSE L3

-- 
Yours,
Muchun