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

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Date:	Wed, 27 Apr 2011 14:39:53 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Andrea Righi <andrea@...terlinux.com>,
	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 14:33, Matthew Wilcox wrote:
> On Wed, Apr 27, 2011 at 08:13:47PM +0200, Andrea Righi wrote:
>> @@ -127,6 +128,12 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
>>                       invalidate_mapping_pages(mapping, start_index,
>>                                               end_index);
>>               break;
>> +     case POSIX_FADV_DONTNEED_FS:
>> +             if (capable(CAP_SYS_ADMIN))
>> +                     drop_pagecache_sb(file->f_dentry->d_sb, NULL);
>> +             else
>> +                     ret = -EPERM;
>> +             break;
>>       default:
>>               ret = -EINVAL;
>>       }
>
> Mmm ... what if I open /dev/sdxyz and call fadvise() on it?  I think
> you end up flushing /dev's page cache entries, instead of the filesystem
> which is on /dev/sdxyz.

i was thinking of that, but was trying to come up with situations
where there might not have a node to work on.  fs's in a file go
through loop devs, dm/lvm have ones created, and flash fs's still have
a mtd block.  how about network based fs's ?  how you going to signal
dropping of pages for nfs or cifs or fuse ones ?
-mike
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