From: Yang Shi <shy828301@gmail.com>
To: David Hildenbrand <david@redhat.com>
Cc: Peter Xu <peterx@redhat.com>,
Linux Memory Management List <linux-mm@kvack.org>,
Minchan Kim <minchan@kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Rik van Riel <riel@surriel.com>,
Michal Hocko <mhocko@kernel.org>,
Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: Page zapping and page table reclaim
Date: Fri, 19 Mar 2021 10:04:00 -0700 [thread overview]
Message-ID: <CAHbLzkri0u076G2qsAjKGKzTQzMjTVt3Kxoq_-_3GU4-HoOoMQ@mail.gmail.com> (raw)
In-Reply-To: <634820ea-33bf-7423-cdea-ab3e63aa9729@redhat.com>
On Thu, Mar 11, 2021 at 1:35 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 11.03.21 22:26, Peter Xu wrote:
> > On Thu, Mar 11, 2021 at 07:14:02PM +0100, David Hildenbrand wrote:
> >> I was wondering, is there any mechanism that reclaims basically empty page
> >> tables in a running process?
> >
> > Would munmap() count? :)
>
> Haha, no -- also not mmap(FIXED) or mremap(FIXED) ;)
>
> As so often lately, the use case is sparse memory mappings where we
>
> a) may want to reuse the area later.
> b) don't want to hold the mmap lock in write while optimizing
> c) don't want to create a lot of individual mappings that we might not
> be able to merge again.
Will the below work for you?
1. acquire write mmap lock
2. unlink vmas from the list and rbtree (so the vmas won't be visible
to any concurrent readers/writers)
3. downgrade write lock to read lock
4. zap page tables and free page tables
5. upgrade to write lock
6. relink vmas back to list and rbtree
Actually the current implementation of munmap() does the first 5 steps.
But there is no rwsem upgrade function, so you may have to release the
lock then reacquire the write lock.
>
>
> --
> Thanks,
>
> David / dhildenb
>
>
next prev parent reply other threads:[~2021-03-19 17:04 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-11 18:14 Page zapping and page table reclaim David Hildenbrand
2021-03-11 21:26 ` Peter Xu
2021-03-11 21:35 ` David Hildenbrand
2021-03-19 17:04 ` Yang Shi [this message]
2021-03-22 9:34 ` David Hildenbrand
2021-03-18 16:57 ` Vlastimil Babka
2021-03-18 23:53 ` Balbir Singh
2021-03-19 12:44 ` David Hildenbrand
2021-03-20 1:56 ` Balbir Singh
2021-03-22 9:19 ` David Hildenbrand
2021-03-18 18:03 ` Rik van Riel
2021-03-18 18:15 ` David Hildenbrand
2021-03-24 9:55 ` David Hildenbrand
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