From: David Hildenbrand <david@redhat.com>
To: Qi Zheng <zhengqi.arch@bytedance.com>,
akpm@linux-foundation.org, tglx@linutronix.de,
hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, songmuchun@bytedance.com
Subject: Re: [PATCH 0/7] Free user PTE page table pages
Date: Mon, 19 Jul 2021 09:34:20 +0200 [thread overview]
Message-ID: <5ce5fb25-df1d-b807-8807-595b8a7bfc63@redhat.com> (raw)
In-Reply-To: <20210718043034.76431-1-zhengqi.arch@bytedance.com>
On 18.07.21 06:30, Qi Zheng wrote:
> Hi,
>
> This patch series aims to free user PTE page table pages when all PTE entries
> are empty.
>
> The beginning of this story is that some malloc libraries(e.g. jemalloc or
> tcmalloc) usually allocate the amount of VAs by mmap() and do not unmap those VAs.
> They will use madvise(MADV_DONTNEED) to free physical memory if they want.
> But the page tables do not be freed by madvise(), so it can produce many
> page tables when the process touches an enormous virtual address space.
... did you see that I am actually looking into this?
https://lkml.kernel.org/r/bae8b967-c206-819d-774c-f57b94c4b362@redhat.com
and have already spent a significant time on it as part of my research,
which is *really* unfortunate and makes me quite frustrated at the
beginning of the week alreadty ...
Ripping out page tables is quite difficult, as we have to stop all page
table walkers from touching it, including the fast_gup, rmap and page
faults. This usually involves taking the mmap lock in write. My approach
does page table reclaim asynchronously from another thread and do not
rely on reference counts.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-07-19 7:34 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-18 4:30 [PATCH 0/7] Free user PTE page table pages Qi Zheng
2021-07-18 4:30 ` [PATCH 1/7] mm: fix the deadlock in finish_fault() Qi Zheng
2021-07-18 21:28 ` Kirill A. Shutemov
2021-07-19 9:53 ` Qi Zheng
2021-07-20 23:14 ` Andrew Morton
2021-07-21 2:21 ` Qi Zheng
2021-07-18 4:30 ` [PATCH 2/7] mm: introduce pte_install() helper Qi Zheng
2021-07-18 21:31 ` Kirill A. Shutemov
2021-07-19 10:20 ` Qi Zheng
2021-07-18 4:30 ` [PATCH 3/7] mm: remove redundant smp_wmb() Qi Zheng
2021-07-27 13:39 ` Muchun Song
2021-07-18 4:30 ` [PATCH 4/7] mm: rework the parameter of lock_page_or_retry() Qi Zheng
2021-07-18 4:30 ` [PATCH 5/7] mm: free user PTE page table pages Qi Zheng
2021-07-18 6:19 ` Mika Penttilä
2021-07-19 12:56 ` Qi Zheng
2021-07-19 13:55 ` Mika Penttilä
2021-07-19 14:12 ` Qi Zheng
2021-07-19 14:17 ` Mika Penttilä
2021-07-18 22:01 ` Kirill A. Shutemov
2021-07-19 13:55 ` Qi Zheng
2021-07-18 4:30 ` [PATCH 6/7] mm: defer freeing PTE page table for a grace period Qi Zheng
2021-07-18 4:30 ` [PATCH 7/7] mm: use mmu_gather to free PTE page table Qi Zheng
2021-07-19 7:34 ` David Hildenbrand [this message]
2021-07-19 11:28 ` [PATCH 0/7] Free user PTE page table pages David Hildenbrand
2021-07-19 12:42 ` Muchun Song
2021-07-19 13:30 ` Muchun Song
2021-07-20 4:00 ` Qi Zheng
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