Date: Mon, 10 Feb 2014 13:35:35 -0800 (PST)
From: David Rientjes <rientjes@google.com>
To: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
cc: Andrew Morton <akpm@linux-foundation.org>,
        Fengguang Wu <fengguang.wu@intel.com>,
        David Cohen <david.a.cohen@linux.intel.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Damien Ramonda <damien.ramonda@intel.com>, Jan Kara <jack@suse.cz>,
        Linus Torvalds <torvalds@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH V5] mm readahead: Fix readahead fail for no local
 memory and limit readahead pages
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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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