From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Frysinger <vapier-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH v2] fadvise: introduce POSIX_FADV_DONTNEED_FS
Date: Wed, 27 Apr 2011 14:39:53 -0400
Message-ID: <BANLkTinPTPMWPN+JELtCZDjrVepLetX6FQ@mail.gmail.com>
References: <1303928027-5100-1-git-send-email-andrea@betterlinux.com> <20110427183308.GA16716@parisc-linux.org>
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Cc: Andrea Righi <andrea-oIIqvOZpAevzfdHfmsDf5w@public.gmane.org>,
	Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Dave Chinner <david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org>,
	Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
	Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
To: Matthew Wilcox <matthew-Ztpu424NOJ8@public.gmane.org>
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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 off=
set, loff_t len, int advice)
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
 =C2=A0 invalidate_mapping_pages(mapping, start_index,
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0=
 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 end_index);
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 break;
>> + =C2=A0 =C2=A0 case POSIX_FADV_DONTNEED_FS:
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (capable(CAP_SYS_ADMI=
N))
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 drop_pagecache_sb(file->f_dentry->d_sb, NULL);
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 else
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 ret =3D -EPERM;
>> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 break;
>> =C2=A0 =C2=A0 =C2=A0 default:
>> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 ret =3D -EINVAL;
>> =C2=A0 =C2=A0 =C2=A0 }
>
> Mmm ... what if I open /dev/sdxyz and call fadvise() on it? =C2=A0I t=
hink
> you end up flushing /dev's page cache entries, instead of the filesys=
tem
> 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