linux-kernel - Re: [PATCH] mm/fadvise: discard partial pages iff endbyte is also eof

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Date:   Thu, 04 Jan 2018 15:44:20 +0800
From:   "夷则(Caspar)" <jinli.zjl@...baba-inc.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     "Andrew Morton" <akpm@...ux-foundation.org>,
        <green@...uxhacker.ru>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        "杨勇(智彻)" <zhiche.yy@...baba-inc.com>,
        "十刀" <shidao.ytt@...baba-inc.com>
Subject: Re: [PATCH] mm/fadvise: discard partial pages iff endbyte is also eof



On 2018/1/4 14:13, 夷则(Caspar) wrote:
> 
> This patch is trying to help to solve a real issue. Sometimes we need to 
> evict the whole file from page cache because we are sure it will not be 
> used in the near future. We try to use posix_fadvise() to finish our 
> work but we often see a "small tail" at the end of some files could not 
> be evicted, after digging a little bit, we find those file sizes are not 
> page-aligned and the "tail" turns out to be partial pages.
> 
> We fail to find a standard from posix_fadvise() manual page to subscribe 
> the function behaviors if the `offset' and `len' params are not 

Oops, I find a 'standard' documented in latest man-pages.git[1], blame 
my centos7, it runs with an old man-pages.rpm :-(

Thanks,
Caspar

[1] 
https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?h=ceb1c326b9f3e863dfd9bf33bc7118bb1fa29bfc

> page-aligned, then we go to kernel tree and see this:
> 
>          /*
>           * First and last FULL page! Partial pages are deliberately
>           * preserved on the expectation that it is better to preserve
>           * needed memory than to discard unneeded memory.
>           */