linux-kernel - Re: [PATCH v2] fadvise: introduce POSIX_FADV_DONTNEED

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Message-ID: <BANLkTinG+ooNRH-VUjKdaHixbGCwk5XoXA@mail.gmail.com>
Date:	Wed, 27 Apr 2011 14:25:17 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	Andrea Righi <andrea@...terlinux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, linux-fsdevel@...r.kernel.org,
	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fadvise: introduce POSIX_FADV_DONTNEED_FS

On Wed, Apr 27, 2011 at 14:13, Andrea Righi wrote:
> Introduce a new fadvise flag to drop page cache pages of a single
> filesystem.
>
> At the moment it is possible to drop page cache pages via
> /proc/sys/vm/drop_pagecache or via posix_fadvise(POSIX_FADV_DONTNEED).
>
> The first method drops the whole page cache while the second can be used
> to drop page cache pages of a single file descriptor. However, there's
> not a simple way to drop all the pages of a filesystem (we could scan
> all the file descriptors and use posix_fadvise(POSIX_FADV_DONTNEED), but
> this solution obviously doesn't scale well).

what if you open the mount point and use POSIX_FADV_DONTNEED on that
dir handle ?  if you required write access for that level, it'd also
implicitly take care of the permission issue.  but maybe this is just
trying to fit existing code in the wrong way.
-mike
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