From: Matthew Wilcox <willy@infradead.org>
To: Yang Shi <yang.shi@linux.alibaba.com>
Cc: mhocko@kernel.org, ldufour@linux.vnet.ibm.com, vbabka@suse.cz,
kirill@shutemov.name, akpm@linux-foundation.org,
dave.hansen@intel.com, oleg@redhat.com,
srikar@linux.vnet.ibm.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC v10 PATCH 0/3] mm: zap pages with read mmap_sem in munmap for large mapping
Date: Tue, 18 Sep 2018 03:37:57 -0700 [thread overview]
Message-ID: <20180918103757.GA17108@bombadil.infradead.org> (raw)
In-Reply-To: <d00aea15-cf08-1980-dcdf-bf24334e6848@linux.alibaba.com>
On Mon, Sep 17, 2018 at 01:00:58PM -0700, Yang Shi wrote:
> On 9/15/18 3:10 AM, Matthew Wilcox wrote:
> > Something I've been wondering about for a while is whether we should "sort"
> > the readers together. ie if the acquirers look like this:
> >
> > A write
> > B read
> > C read
> > D write
> > E read
> > F read
> > G write
> >
> > then we should grant the lock to A, BCEF, D, G rather than A, BC, D, EF, G.
>
> I'm not sure how much this can help to the real world workload.
>
> Typically, there are multi threads to contend for one mmap_sem. So, they are
> trying to read/write the same address space. There might be dependency or
> synchronization among them. Sorting read together might break the
> dependency?
I don't think that's true for the mmap_sem. If one thread is trying to
get the sem for read then it's a page fault. Another thread trying to
get the sem for write is trying to modify the address space. If an
application depends on the ordering of an mmap vs a page fault, it has
to have its own synchronisation.
prev parent reply other threads:[~2018-09-18 10:38 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-14 20:34 [RFC v10 PATCH 0/3] mm: zap pages with read mmap_sem in munmap for large mapping Yang Shi
2018-09-14 20:34 ` [RFC v10 PATCH 1/3] mm: mmap: zap pages with read mmap_sem in munmap Yang Shi
2018-09-15 9:21 ` Matthew Wilcox
2018-09-17 19:49 ` Yang Shi
2018-09-14 20:34 ` [RFC v10 PATCH 2/3] mm: unmap VM_HUGETLB mappings with optimized path Yang Shi
2018-09-15 9:44 ` Matthew Wilcox
2018-09-14 20:34 ` [RFC v10 PATCH 3/3] mm: unmap VM_PFNMAP " Yang Shi
2018-09-15 9:45 ` Matthew Wilcox
2018-09-15 10:10 ` [RFC v10 PATCH 0/3] mm: zap pages with read mmap_sem in munmap for large mapping Matthew Wilcox
2018-09-17 20:00 ` Yang Shi
2018-09-18 10:37 ` Matthew Wilcox [this message]
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