From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 30 Jan 2003 03:06:58 +0100 From: Andrea Arcangeli Subject: Re: Linus rollup Message-ID: <20030130020658.GW1237@dualathlon.random> References: <20030129022617.62800a6e.akpm@digeo.com> <1043879752.10150.387.camel@dell_ss3.pdx.osdl.net> <20030129151206.269290ff.akpm@digeo.com> <20030129.163034.130834202.davem@redhat.com> <20030129172743.1e11d566.akpm@digeo.com> <20030130013522.GP1237@dualathlon.random> <20030129180054.03ac0d48.akpm@digeo.com> <20030129175232.A19969@twiddle.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030129175232.A19969@twiddle.net> Sender: owner-linux-mm@kvack.org Return-Path: To: Richard Henderson Cc: Andrew Morton , davem@redhat.com, shemminger@osdl.org, rmk@arm.linux.org.uk, ak@muc.de, davidm@napali.hpl.hp.com, anton@samba.org, linux-mm@kvack.org List-ID: On Wed, Jan 29, 2003 at 05:52:32PM -0800, Richard Henderson wrote: > On Wed, Jan 29, 2003 at 06:00:54PM -0800, Andrew Morton wrote: > > Andrea Arcangeli wrote: > > > if we hold the spinlock, the serialized memory can't be change under us, > > > so there's no need to put a read barrier, we only care that pre_sequence > > > is visible before the chagnes are visible and before post_sequence is > > > visible, hence only wmb() (after spin_lock and pre_sequence++) is > > > needed there and only rmb() is needed in the read-side. > > Hmm. Perhaps I was confused about how these things are intended > to be used. If indeed the writer doesn't care about the order > in which pre/post_sequence are accessed, then wmb is sufficient > to keep their updates ordered. yep, IMHO it should be enough. btw, I'm speaking only about the fr_write_lock/unlock, not sure what the write_begin/end are meant for, there are no fr_write_begin/end in the patch I was reading (in 2.4). If fr_write_begin/end have to be retained because they can do something useful, and they don't take the spinlock, it could be needed there to use mb(), I just have no idea of where write_begin/end could be useful so it's hard to say. Andrea -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/