linux-kernel - Re: [PATCH 16/16] mm: pass get_user_pages_fast iterator arguments in a structure

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Date:   Wed, 12 Jun 2019 10:52:53 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Christoph Hellwig <hch@....de>,
        James Hogan <jhogan@...nel.org>,
        Paul Burton <paul.burton@...s.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>
Cc:     Andrey Konovalov <andreyknvl@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-sh@...r.kernel.org, Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>, sparclinux@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH 16/16] mm: pass get_user_pages_fast iterator arguments in
 a structure

Christoph Hellwig's on June 12, 2019 12:41 am:
> Instead of passing a set of always repeated arguments down the
> get_user_pages_fast iterators, create a struct gup_args to hold them and
> pass that by reference.  This leads to an over 100 byte .text size
> reduction for x86-64.

What does this do for performance? I've found this pattern can be
bad for store aliasing detection.

Thanks,
Nick