From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH v5 01/11] asm-generic/pgtable: Adds generic functions to
 monitor lockless pgtable walks
Date: Tue, 8 Oct 2019 17:47:06 +0300
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To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Song Liu <songliubraving@fb.com>, Michal Hocko <mhocko@suse.com>, Peter Zijlstra <peterz@infradead.org>, "Dmitry V. Levin" <ldv@altlinux.org>, Keith Busch <keith.busch@intel.com>, linux-mm@kvack.org, Paul Mackerras <paulus@samba.org>, Christoph Lameter <cl@linux.com>, Ira Weiny <ira.weiny@intel.com>, Dan Williams <dan.j.williams@intel.com>, Elena Reshetova <elena.reshetova@intel.com>, linux-arch@vger.kernel.org, Santosh Sivaraj <santosh@fossix.org>, Davidlohr Bueso <dave@stgolabs.net>, Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>, Mike Rapoport <rppt@linux.ibm.com>, Jason Gunthorpe <jgg@ziepe.ca>, Vlastimil Babka <vbabka@suse.cz>, Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>, Leonardo Bras <leonardo@linux.ibm.com>, Alexey Dobriyan <adobriyan@gmail.com>, Ingo Molnar <mingo@kernel.org>, Andrea Arcangeli <aarcange@redhat.com>, Ralph Campbell <rcampbell@nvidia.com>
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On Sat, Oct 05, 2019 at 02:05:29PM +0530, Aneesh Kumar K.V wrote:
> MADV_DONTNEED has caused us multiple issues due to the fact that it can run
> in parallel to page fault. I am not sure whether we have a known/noticeable
> performance gain in allowing that with mmap_sem held in read mode.

Yes we do. MADV_DONTNEED used a lot by userspace memory allocators and it
will be very noticible performance regression if we would switch it to
down_write(mmap_sem).

-- 
 Kirill A. Shutemov