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From:   Wei Wang <wvw@google.com>
Date:   Fri, 16 Mar 2018 22:13:19 +0000
Message-ID: <CAGXk5yoL=NuW1d1VHD9_CXi3kg0gmKeWFubNC7Ro053yDnR9vA@mail.gmail.com>
Subject: Re: [PATCH] mm: add config for readahead window
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Wei Wang <wei.vince.wang@gmail.com>, gregkh@linuxfoundation.org,
        Todd Poynor <toddpoynor@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Michal Hocko <mhocko@suse.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Jan Kara <jack@suse.cz>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Hugh Dickins <hughd@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Sherry Cheung <SCheung@nvidia.com>,
        "Oliver O'Halloran" <oohall@gmail.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Huang Ying <ying.huang@intel.com>,
        Dennis Zhou <dennisz@fb.com>,
        Pavel Tatashin <pasha.tatashin@oracle.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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On Fri, Mar 16, 2018 at 2:59 PM Andrew Morton <akpm@linux-foundation.org>
wrote:

> On Fri, 16 Mar 2018 21:51:48 +0000 Wei Wang <wei.vince.wang@gmail.com>
wrote:

> > On Fri, Mar 16, 2018, 14:33 Andrew Morton <akpm@linux-foundation.org>
wrote:
> >
> > > On Fri, 16 Mar 2018 11:25:08 -0700 Wei Wang <wvw@google.com> wrote:
> > >
> > > > Change VM_MAX_READAHEAD value from the default 128KB to a
configurable
> > > > value. This will allow the readahead window to grow to a maximum
size
> > > > bigger than 128KB during boot, which could benefit to sequential
read
> > > > throughput and thus boot performance.
> > >
> > > You can presently run ioctl(BLKRASET) against the block device?
> > >
> >
> > Yeah we are doing tuning in userland after init. But this is something
we
> > thought could help in very early stage.
> >

> "thought" and "could" are rather weak!  Some impressive performance
> numbers for real-world setups would help such a patch along.

~90ms savings from an Android device compared to setting the window later
in userland.
I was using 'week' words as I agree with Linus's point - it is all about
the storage, so the savings are not universal indeed.