linux-kernel - Re: [PATCH 8/8] mm: enable maple tree RCU mode by default.

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Message-ID: <ZDTFCOg7/I1WIviR@casper.infradead.org>
Date:   Tue, 11 Apr 2023 03:25:12 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     kernel test robot <oliver.sang@...el.com>
Cc:     "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        oe-lkp@...ts.linux.dev, lkp@...el.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        ying.huang@...el.com, feng.tang@...el.com, fengwei.yin@...el.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        maple-tree@...ts.infradead.org,
        Suren Baghdasaryan <surenb@...gle.com>, stable@...r.kernel.org,
        syzbot+8d95422d3537159ca390@...kaller.appspotmail.com
Subject: Re: [PATCH 8/8] mm: enable maple tree RCU mode by default.

On Tue, Apr 11, 2023 at 09:25:16AM +0800, kernel test robot wrote:
> kernel test robot noticed a -8.5% regression of stress-ng.mmapaddr.ops_per_sec on:

Assuming this is the test in question:

https://github.com/ColinIanKing/stress-ng/blob/master/stress-mmapaddr.c

then yes, this is expected.  The test calls mmap() and munmap() a lot,
and we've made those slower in order to fix a bug.

While it does take pagefaults (which is a better test than some
microbenchmarks), it only takes one pagefault per call to mmap() and
munmap(), which is not representative of real workloads.

Thanks for running the test.