linux-kernel - Re: [RFC PATCH V5] mm readahead: Fix readahead fail for no local memory and limit readahead pages

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Date:	Fri, 14 Feb 2014 08:43:05 +0100
From:	Jan Kara <jack@...e.cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>,
	David Rientjes <rientjes@...gle.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	David Cohen <david.a.cohen@...ux.intel.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Damien Ramonda <damien.ramonda@...el.com>,
	Jan Kara <jack@...e.cz>, linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH V5] mm readahead: Fix readahead fail for no local
 memory and limit readahead pages

On Thu 13-02-14 16:37:53, Linus Torvalds wrote:
> Is this whole thread still just for the crazy and pointless
> "max_sane_readahead()"?
> 
> Or is there some *real* reason we should care?
> 
> Because if it really is just for max_sane_readahead(), then for the
> love of God, let us just do this
> 
>  unsigned long max_sane_readahead(unsigned long nr)
>  {
>         return min(nr, 128);
>  }
> 
> and bury this whole idiotic thread.
  max_sane_readahead() is also used for limiting amount of readahead for
[fm]advice(2) WILLNEED and that is used e.g. by a dynamic linker to preload
shared libraries into memory. So I'm convinced this usecase *will* notice
the change - effectively we limit preloading of shared libraries to the
first 512KB in the file but libraries get accessed in a rather random manner.

Maybe limits for WILLNEED and for standard readahead should be different.
It makes sence to me and people seem to keep forgetting that
max_sane_readahead() limits also WILLNEED preloading.

								Honza

> On Thu, Feb 13, 2014 at 4:14 PM, Nishanth Aravamudan
> <nacc@...ux.vnet.ibm.com> wrote:
> >
> > I'm working on this latter bit now. I tried to mirror ia64, but it looks
> > like they have CONFIG_USER_PERCPU_NUMA_NODE_ID, which powerpc doesn't.
> > It seems like CONFIG_USER_PERCPU_NUMA_NODE_ID and
> > CONFIG_HAVE_MEMORYLESS_NODES should be tied together in Kconfig?
> >
> > I'll keep working, but would appreciate any further insight.
> >
> > -Nish
> >
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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