From: Muchun Song <songmuchun@bytedance.com>
To: Oscar Salvador <osalvador@suse.de>
Cc: "Mike Kravetz" <mike.kravetz@oracle.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"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>,
"HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>,
"Joao Martins" <joao.m.martins@oracle.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 v16 4/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page
Date: Wed, 24 Feb 2021 11:47:49 +0800 [thread overview]
Message-ID: <CAMZfGtUBMzAgPVgm=9wgJg+yytxwSGOK_BVOw93RPLb3_tFS_g@mail.gmail.com> (raw)
In-Reply-To: <20210223223157.GA2740@localhost.localdomain>
On Wed, Feb 24, 2021 at 6:32 AM Oscar Salvador <osalvador@suse.de> wrote:
>
> On Tue, Feb 23, 2021 at 04:41:28PM +0100, Oscar Salvador wrote:
> > On Tue, Feb 23, 2021 at 11:50:05AM +0100, Oscar Salvador wrote:
> > > > CPU0: CPU1:
> > > > set_compound_page_dtor(HUGETLB_PAGE_DTOR);
> > > > memory_failure_hugetlb
> > > > get_hwpoison_page
> > > > __get_hwpoison_page
> > > > get_page_unless_zero
> > > > put_page_testzero()
> > > >
> > > > Maybe this can happen. But it is a very corner case. If we want to
> > > > deal with this. We can put_page_testzero() first and then
> > > > set_compound_page_dtor(HUGETLB_PAGE_DTOR).
> > >
> > > I have to check further, but it looks like this could actually happen.
> > > Handling this with VM_BUG_ON is wrong, because memory_failure/soft_offline are
> > > entitled to increase the refcount of the page.
> > >
> > > AFAICS,
> > >
> > > CPU0: CPU1:
> > > set_compound_page_dtor(HUGETLB_PAGE_DTOR);
> > > memory_failure_hugetlb
> > > get_hwpoison_page
> > > __get_hwpoison_page
> > > get_page_unless_zero
> > > put_page_testzero()
> > > identify_page_state
> > > me_huge_page
> > >
> > > I think we can reach me_huge_page with either refcount = 1 or refcount =2,
> > > depending whether put_page_testzero has been issued.
> > >
> > > For now, I would not re-enqueue the page if put_page_testzero == false.
> > > I have to see how this can be handled gracefully.
> >
> > I took a brief look.
> > It is not really your patch fault. Hugetlb <-> memory-failure synchronization is
> > a bit odd, it definitely needs improvment.
> >
> > The thing is, we can have different scenarios here.
> > E.g: by the time we return from put_page_testzero, we might have refcount ==
> > 0 and PageHWPoison, or refcount == 1 PageHWPoison.
> >
> > The former will let a user get a page from the pool and get a sigbus
> > when it faults in the page, and the latter will be even more odd as we
> > will have a self-refcounted page in the free pool (and hwpoisoned).
I have been looking at the dequeue_huge_page_node_exact().
If a PageHWPoison huge page is in the free pool list, the page will
not be allocated to the user. The PageHWPoison huge page
will be skip in the dequeue_huge_page_node_exact().
> >
> > As I said, it is not this patchset fault. I just made me realize this
> > problem.
> >
> > I have to think some more about this.
>
> I have been thinking more about this.
> memory failure events can occur at any time, and we might not be in a
> position where we can handle gracefully the error, meaning that the page
> might end up in non desirable state.
>
> E.g: we could flag the page right before enqueing it.
>
> I still think that VM_BUG_ON should go, as the refcount can be perfectly
> increased by memory-failure/soft_offline handlers, so BUGing there does
> not make much sense.
Make sense. I will remove the VM_BUG_ON.
>
> One think we could do is to check the state of the page we want to
> retrieve from the free hugepage pool.
> We should discard any HWpoisoned ones, and dissolve them.
>
> The thing is, memory-failure/soft_offline should allocate a new hugepage
> for the free pool, so keep the pool stable.
> Something like [1].
>
> Anyway, this is orthogonal to this patch, and something I will work on
> soon.
>
> [1] https://lore.kernel.org/linux-mm/20210222135137.25717-2-osalvador@suse.de/T/#u
Thanks for your efforts on this.
>
> --
> Oscar Salvador
> SUSE L3
next prev parent reply other threads:[~2021-02-24 3:48 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 10:49 [PATCH v16 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
2021-02-19 10:49 ` [PATCH v16 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
2021-02-19 10:49 ` [PATCH v16 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2021-02-19 10:49 ` [PATCH v16 3/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
2021-02-19 10:49 ` [PATCH v16 4/9] mm: hugetlb: alloc " Muchun Song
2021-02-19 14:12 ` Michal Hocko
2021-02-20 4:20 ` [External] " Muchun Song
2021-02-22 9:25 ` Michal Hocko
2021-02-22 10:31 ` Muchun Song
2021-02-22 10:50 ` Oscar Salvador
2021-02-23 0:00 ` Mike Kravetz
2021-02-23 5:35 ` [External] " Muchun Song
2021-02-23 9:27 ` Oscar Salvador
2021-02-23 10:27 ` [External] " Muchun Song
2021-02-23 10:50 ` Oscar Salvador
2021-02-23 15:41 ` Oscar Salvador
2021-02-23 22:31 ` Oscar Salvador
2021-02-24 3:47 ` Muchun Song [this message]
2021-02-24 8:31 ` Oscar Salvador
2021-02-19 10:49 ` [PATCH v16 5/9] mm: hugetlb: set the PageHWPoison to the raw error page Muchun Song
2021-02-19 10:49 ` [PATCH v16 6/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
2021-02-19 10:49 ` [PATCH v16 7/9] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
2021-02-19 10:49 ` [PATCH v16 8/9] mm: hugetlb: gather discrete indexes of tail page Muchun Song
2021-02-19 10:49 ` [PATCH v16 9/9] mm: hugetlb: optimize the code with the help of the compiler Muchun Song
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