linux-kernel - Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries

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Message-ID: <CA+55aFzfQz7c8pcMfLDaRNReNF2HaKJGoWpgB6caQjNAyjg-hA@mail.gmail.com>
Date:   Thu, 12 Jul 2018 11:06:08 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     James Bottomley <James.Bottomley@...senpartnership.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Waiman Long <longman@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Jan Kara <jack@...e.cz>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        "Wangkai (Kevin,C)" <wangkai86@...wei.com>
Subject: Re: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries

On Thu, Jul 12, 2018 at 10:21 AM James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
>
> On Thu, 2018-07-12 at 09:49 -0700, Matthew Wilcox wrote:
> >
> > I don't know that it does work.  Or that it works well.
>
> I'm not claiming the general heuristics are perfect (in fact I know we
> still have a lot of problems with dirty reclaim and writeback).

I think this whole "this is about running out of memory" approach is wrong.

We *should* handle that well. Or well enough in practice, at least.

Do we? Maybe not. Should the dcache be the one area to be policed and
worked around? Probably not.

But there may be other reasons to just limit negative dentries.

What does the attached program do to people? It's written to be
intentionally annoying to the dcache.

               Linus

View attachment "t.c" of type "text/x-csrc" (617 bytes)