linux-kernel - Re: [PATCH 2/3] mm/filemap: initiate readahead even if IOCB

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Message-ID: <CAHk-=wg0FXvwB09WJaZk039CfQ0hEnyES_ANE392dfsx6U8WUQ@mail.gmail.com>
Date:   Thu, 31 Jan 2019 23:05:32 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     Michal Hocko <mhocko@...nel.org>, Jiri Kosina <jikos@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux API <linux-api@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Jann Horn <jannh@...gle.com>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Andy Lutomirski <luto@...capital.net>,
        Kevin Easton <kevin@...rana.org>,
        Matthew Wilcox <willy@...radead.org>,
        Cyril Hrubis <chrubis@...e.cz>, Tejun Heo <tj@...nel.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Daniel Gruss <daniel@...ss.cc>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 2/3] mm/filemap: initiate readahead even if IOCB_NOWAIT is
 set for the I/O

On Thu, Jan 31, 2019 at 9:16 PM Dave Chinner <david@...morbit.com> wrote:
>
> You are conflating "best effort non-blocking operation" with
> "atomic guarantee".  RWF_NOWAIT/IOCB_NOWAIT is the
> former, not the latter.

Right.

That's my *point*, Dave.

It's not 'atomic guarantee", and never will be. We are in 100%
agreement. That's what I _said_.

And part of "best effort" is very much "not a security information leak".

I really don't see why you are so argumentative.

As I mentioned earlier in the thread, it's actually quite possible
that users will actually find that starting read-ahead is a *good*
thing, Dave.

Even - in fact *particularly* - the user you brought up: samba using
RWF_NOWAIT to try to do things synchronously quickly.

So Dave, why are you being so negative?

             Linus