From: Michal Hocko <email@example.com>
To: Mike Kravetz <firstname.lastname@example.org>
Cc: Matthew Wilcox <email@example.com>,
Andrew Morton <firstname.lastname@example.org>,
"Aneesh Kumar K.V" <email@example.com>,
Subject: Re: [RFC PATCH] mm/hugetlb: make hugetlb_lock irq safe
Date: Thu, 6 Sep 2018 13:19:04 +0200 [thread overview]
Message-ID: <20180906111904.GB26069@dhcp22.suse.cz> (raw)
On Wed 05-09-18 16:51:00, Mike Kravetz wrote:
> On 09/05/2018 04:07 PM, Matthew Wilcox wrote:
> > On Wed, Sep 05, 2018 at 03:00:08PM -0700, Andrew Morton wrote:
> >> On Wed, 5 Sep 2018 14:35:11 -0700 Mike Kravetz <firstname.lastname@example.org> wrote:
> >>>> so perhaps we could put some
> >>>> stopgap workaround into that site and add a runtime warning into the
> >>>> put_page() code somewhere to detect puttage of huge pages from hardirq
> >>>> and softirq contexts.
> >>> I think we would add the warning/etc at free_huge_page. The issue would
> >>> only apply to hugetlb pages, not THP.
> >>> But, the more I think about it the more I think Aneesh's patch to do
> >>> spin_lock/unlock_irqsave is the right way to go. Currently, we only
> >>> know of one place where a put_page of hugetlb pages is done from softirq
> >>> context. So, we could take the spin_lock/unlock_bh as Matthew suggested.
> >>> When the powerpc iommu code was added, I doubt this was taken into account.
> >>> I would be afraid of someone adding put_page from hardirq context.
> >> Me too. If we're going to do this, surely we should make hugepages
> >> behave in the same fashion as PAGE_SIZE pages.
> > But these aren't vanilla hugepages, they're specifically hugetlbfs pages.
> > I don't believe there's any problem with calling put_page() on a normally
> > allocated huge page or THP.
> The powerpc iommu code (at least) treated hugetlbfs pages as any other page
> (huge, THP or base) and called put_page from softirq context.
> It seems there are at least two ways to address this:
> 1) Prohibit this behavior for hugetlbfs pages
> 2) Try to make hugetlbfs pages behave like other pages WRT put_page
Hugetlb pages have always been special and that has caused us more
headache than necessary. So if there is a user calling put_page from the
soft IRQ context (which is a news to me) then we can expect somebody
will do that from the hard IRQ context sooner or later. So rather than
make hugetlb a special snow flake again I vote for 2) and make it
consistent with other pages.
next prev parent reply other threads:[~2018-09-06 11:19 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-05 11:23 [RFC PATCH] mm/hugetlb: make hugetlb_lock irq safe Aneesh Kumar K.V
2018-09-05 13:04 ` Matthew Wilcox
2018-09-05 13:26 ` Aneesh Kumar K.V
2018-09-05 13:48 ` Matthew Wilcox
2018-09-05 19:58 ` Andrew Morton
2018-09-05 21:35 ` Mike Kravetz
2018-09-05 22:00 ` Andrew Morton
2018-09-05 23:07 ` Matthew Wilcox
2018-09-05 23:51 ` Mike Kravetz
2018-09-06 4:03 ` Aneesh Kumar K.V
2018-09-06 11:19 ` Michal Hocko [this message]
2018-09-06 3:58 ` Aneesh Kumar K.V
2018-09-06 3:54 ` Aneesh Kumar K.V
2018-09-06 4:00 ` Aneesh Kumar K.V
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