linux-kernel - Re: [PATCH] mm: add config for readahead window

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Date:   Fri, 16 Mar 2018 22:13:19 +0000
From:   Wei Wang <wvw@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Wei Wang <wei.vince.wang@...il.com>, gregkh@...uxfoundation.org,
        Todd Poynor <toddpoynor@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Jan Kara <jack@...e.cz>,
        Jérôme Glisse <jglisse@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Sherry Cheung <SCheung@...dia.com>,
        "Oliver O'Halloran" <oohall@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Huang Ying <ying.huang@...el.com>,
        Dennis Zhou <dennisz@...com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: add config for readahead window

On Fri, Mar 16, 2018 at 2:59 PM Andrew Morton <akpm@...ux-foundation.org>
wrote:

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

> > On Fri, Mar 16, 2018, 14:33 Andrew Morton <akpm@...ux-foundation.org>
wrote:
> >
> > > On Fri, 16 Mar 2018 11:25:08 -0700 Wei Wang <wvw@...gle.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.