From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
"xishi.qiuxishi@alibaba-inc.com" <xishi.qiuxishi@alibaba-inc.com>,
"Chen, Jerry T" <jerry.t.chen@intel.com>,
"Zhuo, Qiuxu" <qiuxu.zhuo@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] mm: hugetlb: soft-offline: dissolve_free_huge_page() return zero on !PageHuge
Date: Wed, 12 Jun 2019 07:09:32 +0000 [thread overview]
Message-ID: <20190612070939.GA25452@hori.linux.bs1.fc.nec.co.jp> (raw)
In-Reply-To: <4a1ea5f4-d35d-f3a6-920c-c35520234aa3@arm.com>
On Tue, Jun 11, 2019 at 03:20:26PM +0530, Anshuman Khandual wrote:
>
> On 06/10/2019 01:48 PM, Naoya Horiguchi wrote:
> > madvise(MADV_SOFT_OFFLINE) often returns -EBUSY when calling soft offline
> > for hugepages with overcommitting enabled. That was caused by the suboptimal
> > code in current soft-offline code. See the following part:
> >
> > ret = migrate_pages(&pagelist, new_page, NULL, MPOL_MF_MOVE_ALL,
> > MIGRATE_SYNC, MR_MEMORY_FAILURE);
> > if (ret) {
> > ...
> > } else {
> > /*
> > * We set PG_hwpoison only when the migration source hugepage
> > * was successfully dissolved, because otherwise hwpoisoned
> > * hugepage remains on free hugepage list, then userspace will
> > * find it as SIGBUS by allocation failure. That's not expected
> > * in soft-offlining.
> > */
> > ret = dissolve_free_huge_page(page);
> > if (!ret) {
> > if (set_hwpoison_free_buddy_page(page))
> > num_poisoned_pages_inc();
> > }
> > }
> > return ret;
> >
> > Here dissolve_free_huge_page() returns -EBUSY if the migration source page
> > was freed into buddy in migrate_pages(), but even in that case we actually
>
> Over committed source pages will be released into buddy and the normal ones
> will not be ? dissolve_free_huge_page() returns -EBUSY because PageHuge()
> return negative on already released pages ?
The answers for both questions here are yes.
> How dissolve_free_huge_page()
> will behave differently with over committed pages. I might be missing some
> recent developments here.
This dissolve_free_huge_page() should see a (free or reused) 4kB page when
overcommitting, and should see a (free or reused) huge page for non
overcommitting case.
>
> > has a chance that set_hwpoison_free_buddy_page() succeeds. So that means
> > current code gives up offlining too early now.
>
> Hmm. It gives up early as the return value from dissolve_free_huge_page(EBUSY)
> gets back as the return code for soft_offline_huge_page() without attempting
> set_hwpoison_free_buddy_page() which still has a chance to succeed for freed
> normal buddy pages.
Exactly.
>
> >
> > dissolve_free_huge_page() checks that a given hugepage is suitable for
> > dissolving, where we should return success for !PageHuge() case because
> > the given hugepage is considered as already dissolved.
>
> Right. It should return 0 (as a success) for freed normal buddy pages. Should
> not it then check explicitly for PageBuddy() as well ?
in new semantics, dissolve_free_huge_page() returns:
0: successfully dissolved free hugepages or the page is already dissolved
EBUSY: failed to dissolved free hugepages or the hugepage is in-use.
so for any types of non hugepages, the return value is 0.
Thanks,
- Naoya
> >
> > This change also affects other callers of dissolve_free_huge_page(),
> > which are cleaned up together.
> >
> > Reported-by: Chen, Jerry T <jerry.t.chen@intel.com>
> > Tested-by: Chen, Jerry T <jerry.t.chen@intel.com>
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > Fixes: 6bc9b56433b76 ("mm: fix race on soft-offlining")
> > Cc: <stable@vger.kernel.org> # v4.19+
> > ---
> > mm/hugetlb.c | 15 +++++++++------
> > mm/memory-failure.c | 5 +----
> > 2 files changed, 10 insertions(+), 10 deletions(-)
> >
> > diff --git v5.2-rc3/mm/hugetlb.c v5.2-rc3_patched/mm/hugetlb.c
> > index ac843d3..048d071 100644
> > --- v5.2-rc3/mm/hugetlb.c
> > +++ v5.2-rc3_patched/mm/hugetlb.c
> > @@ -1519,7 +1519,12 @@ int dissolve_free_huge_page(struct page *page)
> > int rc = -EBUSY;
> >
> > spin_lock(&hugetlb_lock);
> > - if (PageHuge(page) && !page_count(page)) {
> > + if (!PageHuge(page)) {
> > + rc = 0;
> > + goto out;
> > + }
>
> With this early bail out it maintains the functionality when called from
> soft_offline_free_page() for normal pages. For huge page, it continues
> on the previous path.
>
> > +
> > + if (!page_count(page)) {
> > struct page *head = compound_head(page);
> > struct hstate *h = page_hstate(head);
> > int nid = page_to_nid(head);
> > @@ -1564,11 +1569,9 @@ int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
> >
> > for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order) {
> > page = pfn_to_page(pfn);
> > - if (PageHuge(page) && !page_count(page)) {
>
> Right. These checks are now redundant.
>
next prev parent reply other threads:[~2019-06-12 7:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-10 8:18 [PATCH v2 00/02] fix return value issue of soft offlining hugepages Naoya Horiguchi
2019-06-10 8:18 ` [PATCH v2 1/2] mm: soft-offline: return -EBUSY if set_hwpoison_free_buddy_page() fails Naoya Horiguchi
2019-06-10 21:20 ` Andrew Morton
2019-06-10 22:51 ` Naoya Horiguchi
2019-06-11 0:19 ` Mike Kravetz
2019-06-11 0:57 ` Naoya Horiguchi
2019-06-11 8:14 ` Anshuman Khandual
2019-06-12 6:48 ` Naoya Horiguchi
2019-06-10 8:18 ` [PATCH v2 2/2] mm: hugetlb: soft-offline: dissolve_free_huge_page() return zero on !PageHuge Naoya Horiguchi
2019-06-11 9:50 ` Anshuman Khandual
2019-06-12 7:09 ` Naoya Horiguchi [this message]
2019-06-11 17:16 ` Mike Kravetz
2019-06-12 7:24 ` Naoya Horiguchi
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