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

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Message-ID: <alpine.DEB.2.02.1402101333160.15624@chino.kir.corp.google.com>
Date:	Mon, 10 Feb 2014 13:35:35 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
cc:	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>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH V5] mm readahead: Fix readahead fail for no local
 memory and limit readahead pages

On Mon, 10 Feb 2014, Raghavendra K T wrote:

> So I understood that you are suggesting implementations like below
> 
> 1) I do not have problem with the below approach, I could post this in
> next version.
> ( But this did not include 4k limit Linus mentioned to apply)
> 
> unsigned long max_sane_readahead(unsigned long nr)
> {
>         unsigned long local_free_page;
>         int nid;
> 
>         nid = numa_mem_id();
> 
>         /*
>          * We sanitize readahead size depending on free memory in
>          * the local node.
>          */
>         local_free_page = node_page_state(nid, NR_INACTIVE_FILE)
>                           + node_page_state(nid, NR_FREE_PAGES);
>         return min(nr, local_free_page / 2);
> }
> 
> 2) I did not go for below because Honza (Jan Kara) had some
> concerns for 4k limit for normal case, and since I am not
> the expert, I was waiting for opinions.
> 
> unsigned long max_sane_readahead(unsigned long nr)
> {
>         unsigned long local_free_page, sane_nr;
>         int nid;
> 
>         nid = numa_mem_id();
> 	/* limit the max readahead to 4k pages */
> 	sane_nr = min(nr, MAX_REMOTE_READAHEAD);
> 
>         /*
>          * We sanitize readahead size depending on free memory in
>          * the local node.
>          */
>         local_free_page = node_page_state(nid, NR_INACTIVE_FILE)
>                           + node_page_state(nid, NR_FREE_PAGES);
>         return min(sane_nr, local_free_page / 2);
> }
> 

I have no opinion on the 4KB pages, either of the above is just fine.
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