lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Tue, 12 Jan 2021 09:33:35 +0100
From:   Michal Hocko <>
To:     Mike Kravetz <>
Cc:     Muchun Song <>,,,,,
Subject: Re: [PATCH v3 4/6] mm: hugetlb: add return -EAGAIN for

On Mon 11-01-21 17:20:51, Mike Kravetz wrote:
> On 1/10/21 4:40 AM, Muchun Song wrote:
> > There is a race between dissolve_free_huge_page() and put_page(),
> > and the race window is quite small. Theoretically, we should return
> > -EBUSY when we encounter this race. In fact, we have a chance to
> > successfully dissolve the page if we do a retry. Because the race
> > window is quite small. If we seize this opportunity, it is an
> > optimization for increasing the success rate of dissolving page.
> > 
> > If we free a HugeTLB page from a non-task context, it is deferred
> > through a workqueue. In this case, we need to flush the work.
> > 
> > The dissolve_free_huge_page() can be called from memory hotplug,
> > the caller aims to free the HugeTLB page to the buddy allocator
> > so that the caller can unplug the page successfully.
> > 
> > Signed-off-by: Muchun Song <>
> > ---
> >  mm/hugetlb.c | 26 +++++++++++++++++++++-----
> >  1 file changed, 21 insertions(+), 5 deletions(-)
> I am unsure about the need for this patch.  The code is OK, there are no
> issues with the code.
> As mentioned in the commit message, this is an optimization and could
> potentially cause a memory offline operation to succeed instead of fail.
> However, we are very unlikely to ever exercise this code.  Adding an
> optimization that is unlikely to be exercised is certainly questionable.
> Memory offline is the only code that could benefit from this optimization.
> As someone with more memory offline user experience, what is your opinion
> Michal?

I am not a great fun of optimizations without any data to back them up.
I do not see any sign this code has been actually tested and the
condition triggered.

Besides that I have requested to have an explanation of why blocking on
the WQ is safe and that hasn't happened.
Michal Hocko

Powered by blists - more mailing lists