From: David Hildenbrand <david@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
Qi Zheng <zhengqi.arch@bytedance.com>,
akpm@linux-foundation.org, tglx@linutronix.de,
kirill.shutemov@linux.intel.com, mika.penttila@nextfour.com,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, songmuchun@bytedance.com,
zhouchengming@bytedance.com
Subject: Re: [PATCH v3 00/15] Free user PTE page table pages
Date: Wed, 10 Nov 2021 17:53:57 +0100 [thread overview]
Message-ID: <b9ea9c5b-2b7e-a6a9-f1b3-241c0882197c@redhat.com> (raw)
In-Reply-To: <YYv4Msg7zVLS3KE/@casper.infradead.org>
On 10.11.21 17:49, Matthew Wilcox wrote:
> On Wed, Nov 10, 2021 at 04:37:14PM +0100, David Hildenbrand wrote:
>>> I'd suggest to make this new lock a special rwsem which allows either
>>> concurrent read access OR concurrent PTL access, but not both. This
>>
>> I looked into such a lock recently in similar context and something like
>> that does not exist yet (and fairness will be challenging). You either
>> have a single reader or multiple writer. I'd be interested if someone
>> knows of something like that.
>
> We've talked about having such a lock before for filesystems which want
> to permit either many direct-IO accesses or many buffered-IO accesses, but
> want to exclude a mixture of direct-IO and buffered-IO. The name we came
> up with for such a lock was the red-blue lock. Either Team Red has the
> lock, or Team Blue has the lock (or it's free). Indicate free with velue
> zero, Team Red with positive numbers and Team Blue with negative numbers.
> If we need to indicate an opposing team is waiting for the semaphore,
> we can use a high bit (1 << 30) to indicate no new team members can
> acquire the lock. Not sure whether anybody ever coded it up.
Interesting, thanks for sharing!
My excessive google search didn't reveal anything back then (~3 months
ago) -- only questions on popular coding websites asking essentially for
the same thing without any helpful replies. But maybe I used the wrong
keywords (e.g., "multiple reader, multiple writer", I certainly didn't
search for "red-blue lock", but I do like the name :) ).
Fairness might still be the biggest issue, but I am certainly no locking
expert.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-11-10 16:54 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-10 10:54 [PATCH v3 00/15] Free user PTE page table pages Qi Zheng
2021-11-10 10:54 ` [PATCH v3 01/15] mm: do code cleanups to filemap_map_pmd() Qi Zheng
2021-11-10 10:54 ` [PATCH v3 02/15] mm: introduce is_huge_pmd() helper Qi Zheng
2021-11-11 13:46 ` kernel test robot
2021-11-10 10:54 ` [PATCH v3 03/15] mm: move pte_offset_map_lock() to pgtable.h Qi Zheng
2021-11-10 10:54 ` [PATCH v3 04/15] mm: rework the parameter of lock_page_or_retry() Qi Zheng
2021-11-10 10:54 ` [PATCH v3 05/15] mm: add pmd_installed_type return for __pte_alloc() and other friends Qi Zheng
2021-11-10 10:54 ` [PATCH v3 06/15] mm: introduce refcount for user PTE page table page Qi Zheng
2021-11-11 0:37 ` kernel test robot
2021-11-10 10:54 ` [PATCH v3 07/15] mm/pte_ref: add support for user PTE page table page allocation Qi Zheng
2021-11-11 15:17 ` kernel test robot
2021-11-10 10:54 ` [PATCH v3 08/15] mm/pte_ref: initialize the refcount of the withdrawn PTE page table page Qi Zheng
2021-11-10 10:54 ` [PATCH v3 09/15] mm/pte_ref: add support for the map/unmap of user " Qi Zheng
2021-11-10 10:54 ` [PATCH v3 10/15] mm/pte_ref: add support for page fault path Qi Zheng
2021-11-10 10:54 ` [PATCH v3 11/15] mm/pte_ref: take a refcount before accessing the PTE page table page Qi Zheng
2021-11-10 10:54 ` [PATCH v3 12/15] mm/pte_ref: update the pmd entry in move_normal_pmd() Qi Zheng
2021-11-10 10:54 ` [PATCH v3 13/15] mm/pte_ref: free user PTE page table pages Qi Zheng
2021-11-14 14:43 ` [mm/pte_ref] afcc9fb874: kernel_BUG_at_include/linux/pte_ref.h kernel test robot
2021-11-10 10:54 ` [PATCH v3 14/15] Documentation: add document for pte_ref Qi Zheng
2021-11-10 14:39 ` Jonathan Corbet
2021-11-11 5:40 ` Qi Zheng
2021-11-10 10:54 ` [PATCH v3 15/15] mm/pte_ref: use mmu_gather to free PTE page table pages Qi Zheng
2021-11-10 12:56 ` [PATCH v3 00/15] Free user " Jason Gunthorpe
2021-11-10 13:25 ` David Hildenbrand
2021-11-10 13:59 ` Qi Zheng
2021-11-10 14:38 ` Jason Gunthorpe
2021-11-10 15:37 ` David Hildenbrand
2021-11-10 16:39 ` Jason Gunthorpe
2021-11-10 17:37 ` David Hildenbrand
2021-11-10 17:49 ` Jason Gunthorpe
2021-11-11 3:58 ` Qi Zheng
2021-11-11 9:22 ` David Hildenbrand
2021-11-11 11:08 ` Qi Zheng
2021-11-11 11:19 ` David Hildenbrand
2021-11-11 12:00 ` Qi Zheng
2021-11-11 12:20 ` David Hildenbrand
2021-11-11 12:32 ` Qi Zheng
2021-11-11 12:51 ` David Hildenbrand
2021-11-11 13:01 ` Qi Zheng
2021-11-10 16:49 ` Matthew Wilcox
2021-11-10 16:53 ` David Hildenbrand [this message]
2021-11-10 16:56 ` Jason Gunthorpe
2021-11-10 13:54 ` Qi Zheng
-- strict thread matches above, loose matches on Subject: below --
2021-11-10 8:40 Qi Zheng
2021-11-10 8:52 ` Qi Zheng
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