From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH 1/1] [virt] virtio-blk: Use ida to allocate disk index Date: Thu, 16 Jun 2011 09:35:34 +0930 Message-ID: <87hb7qzlm9.fsf@rustcorp.com.au> References: <1306913069-23637-1-git-send-email-dwu@redhat.com> <87mxi1xfz0.fsf@rustcorp.com.au> <4DEF744D.9040702@redhat.com> <87mxhrgba6.fsf@rustcorp.com.au> <20110609091433.GB11773@htj.dyndns.org> <4DF0A374.6090504@redhat.com> <87mxhjzogo.fsf@rustcorp.com.au> <20110615070638.GI8141@htj.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Mark Wu , "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe , Greg Kroah-Hartman To: Tejun Heo Return-path: Received: from ozlabs.org ([203.10.76.45]:60047 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752751Ab1FPBrn (ORCPT ); Wed, 15 Jun 2011 21:47:43 -0400 In-Reply-To: <20110615070638.GI8141@htj.dyndns.org> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, 15 Jun 2011 09:06:38 +0200, Tejun Heo wrote: > It's inherited from idr which was designed to have separate > prepare/allocation stages so that allocation can happen inside an > outer spinlock. It doesn't have too much to do with optimization. > It's mostly to be able to use sleepable context for memory allocation > while allowing atomic id[ra] allocation. It might have made sense for a few callers, but as a general mechanism it stinks. It's a lot of dancing to avoid GFP_ATOMIC allocations; we'd be better making idr_get_new() take a gfp_t, and have an idr_pre_alloc() for those who care. *Sure* there's a chance of racing and we will need to do an atomic allocation. But can anyone justify the current complexity for all callers? > > + * ida_simple_get - get a new id. > > + * @ida: the (initialized) ida. > > + * @min_id: the minimum id (inclusive) > > + * @max_id: the maximum id (inclusive) > > + * > > + * Allocates an id in the range min_id <= id <= max_id, or returns -ENOSPC. > > + * On allocation failure, returns -ENOMEM. This function can sleep. > > + * > > + * Use ida_simple_remove() to get rid of an id. > > + */ > > +int ida_simple_get(struct ida *ida, int min_id, int max_id) > > Hmmm... new interface different from existing id[ra] style, but yeah > something like the above would have made more sense from the > beginning. The only thing is that isn't (begin <= range < end) more > conventional form to express ranges? Yes, but how to express an unlimited range then? I could used unsigned and 0x80000000, but that seemed crude. Cheers, Rusty.