linux-kernel - Re : Re: Re: Re : Re: [PATCH] Squashfs: add asynchronous read support

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Date:	Mon, 23 Dec 2013 12:03:39 +0900
From:	"Chanho Min" <chanho.min@....com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Phillip Lougher <phillip@...ashfs.org.uk>,
	linux-kernel@...r.kernel.org,
	임효준 <hyojun.im@....com>,
	이건호 <gunho.lee@....com>
Subject: Re : Re: Re: Re : Re: [PATCH] Squashfs: add asynchronous read support



> read_pages
>   for(page_idx ...) {
>     if (!add_to_page_cache_lru)) { <-- 1)
>       mapping->a_ops->readpage(filp, page)
>         squashfs_readpage
>           for (i ...) {   2)  Here, 31 pages are inserted into page cache
>             grab_cahe_page_nowait <------/
>               add_to_page_cache_lru
>           }
>     }
>     /*
>      * 1) will be failed with EEXIST by 2) so every pages other than first page
>      * in list would be freed
>      */
>     page_cache_release(page)
>   }
>
> If you see ReadAhead works, it is just by luck as I told you.
> Please simulate it with 64K dd.
You right, This luck happened frequently with 128k dd or my test.

> I understand it but your patch doesn't make it.
>
I think my patch can make it if readahead works normally or luckily.

Thanks a lot!
Chanho,

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