linux-kernel - Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting

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Message-ID: <alpine.LSU.2.11.2012272233170.24487@eggly.anvils>
Date:   Sun, 27 Dec 2020 22:43:44 -0800 (PST)
From:   Hugh Dickins <hughd@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Jan Kara <jack@...e.cz>, Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries
 when prefaulting

On Sun, 27 Dec 2020, Linus Torvalds wrote:
> On Sun, Dec 27, 2020 at 3:48 PM Kirill A. Shutemov <kirill@...temov.name> wrote:
> >
> > I did what Hugh proposed and it got clear to my eyes. It gets somewhat
> > large, but take a look.
> 
> Ok, it's not that much bigger, and the end result is certainly much
> clearer wrt locking.
> 
> So that last version of yours with the fix for the uninitialized 'ret'
> variable looks good to me.
> 
> Of course, I've said that before, and have been wrong. So ...

And guess what... it's broken.

I folded it into testing rc1: segfault on cc1, systemd
"Journal file corrupted, rotating", seen on more than one machine.

I've backed it out, rc1 itself seems fine, I'll leave rc1 under
load overnight, then come back to the faultaround patch tomorrow;
won't glance at it tonight, but maybe Kirill will guess what's wrong.

Hugh