From: Waiman Long <firstname.lastname@example.org>
To: Mike Kravetz <email@example.com>,
Michal Hocko <firstname.lastname@example.org>,
Andrew Morton <email@example.com>,
Matthew Wilcox <firstname.lastname@example.org>,
Subject: Re: [PATCH v2] mm/hugetlb: defer free_huge_page() to a workqueue
Date: Mon, 16 Dec 2019 14:13:40 -0500 [thread overview]
Message-ID: <email@example.com> (raw)
On 12/16/19 2:08 PM, Mike Kravetz wrote:
> On 12/16/19 8:17 AM, Davidlohr Bueso wrote:
>> On Mon, 16 Dec 2019, Michal Hocko wrote:
>>> I am afraid that work_struct is too large to be stuffed into the struct
>>> page array (because of the lockdep part).
>> Yeah, this needs to be done without touching struct page.
>> Which is why I had done the stack allocated way in this patch, but we
>> cannot wait for it to complete in irq, so that's out the window. Andi
>> had suggested percpu allocated work items, but having played with the
>> idea over the weekend, I don't see how we can prevent another page being
>> freed on the same cpu before previous work on the same cpu is complete
>> (cpu0 wants to free pageA, schedules the work, in the mean time cpu0
>> wants to free pageB and workerfn for pageA still hasn't been called).
>>> I think that it would be just safer to make hugetlb_lock irq safe. Are
>>> there any other locks that would require the same?
>> It would be simpler. Any performance issues that arise would probably
>> be only seen in microbenchmarks, assuming we want to have full irq safety.
>> If we don't need to worry about hardirq, then even better.
>> The subpool lock would also need to be irq safe.
> I do think we need to worry about hardirq. There are no restruictions that
> put_page can not be called from hardirq context.
> I am concerned about the latency of making hugetlb_lock (and potentially
> subpool lock) hardirq safe. When these locks were introduced (before my
> time) the concept of making them irq safe was not considered. Recently,
> I learned that the hugetlb_lock is held for a linear scan of ALL hugetlb
> pages during a cgroup reparentling operation. That is just too long.
> If there is no viable work queue solution, then I think we would like to
> restructure the hugetlb locking before a change to just make hugetlb_lock
> irq safe. The idea would be to split the scope of what is done under
> hugetlb_lock. Most of it would never be executed in irq context. Then
> have a small/limited set of functionality that really needs to be irq
> safe protected by an irq safe lock.
Please take a look at my recently posted patch to see if that is an
acceptable workqueue based solution.
next prev parent reply other threads:[~2019-12-16 19:13 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-11 19:46 [PATCH v2] hugetlbfs: Disable softIRQ when taking hugetlb_lock Waiman Long
2019-12-11 22:04 ` Mike Kravetz
2019-12-11 22:19 ` Waiman Long
2019-12-12 1:11 ` Mike Kravetz
2019-12-12 6:06 ` Davidlohr Bueso
2019-12-12 6:30 ` Davidlohr Bueso
2019-12-12 19:04 ` [PATCH v2] mm/hugetlb: defer free_huge_page() to a workqueue Davidlohr Bueso
2019-12-12 19:22 ` Mike Kravetz
2019-12-12 19:36 ` Davidlohr Bueso
2019-12-12 20:52 ` Waiman Long
2019-12-12 21:04 ` Waiman Long
2019-12-16 13:26 ` Michal Hocko
2019-12-16 15:38 ` Waiman Long
2019-12-16 18:44 ` Waiman Long
2019-12-17 9:00 ` Michal Hocko
2019-12-17 18:05 ` Mike Kravetz
2019-12-18 12:18 ` hugetlbfs testing coverage (was: Re: [PATCH v2] mm/hugetlb: defer free_huge_page() to a workqueue) Michal Hocko
2019-12-12 21:01 ` [PATCH v2] mm/hugetlb: defer free_huge_page() to a workqueue Waiman Long
2019-12-16 13:37 ` Michal Hocko
2019-12-16 16:17 ` Waiman Long
2019-12-16 16:17 ` Davidlohr Bueso
2019-12-16 17:18 ` Matthew Wilcox
2019-12-16 19:08 ` Mike Kravetz
2019-12-16 19:13 ` Waiman Long [this message]
2019-12-12 21:32 ` [PATCH v2] hugetlbfs: Disable softIRQ when taking hugetlb_lock Andi Kleen
2019-12-12 22:42 ` Davidlohr Bueso
2019-12-11 23:05 ` Andi Kleen
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