From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx122.postini.com [74.125.245.122]) by kanga.kvack.org (Postfix) with SMTP id 0CB516B002B for ; Wed, 19 Dec 2012 06:56:04 -0500 (EST) Date: Wed, 19 Dec 2012 09:55:58 -0200 From: Rafael Aquini Subject: Re: [RFC 1/2] virtio_balloon: move locking to the balloon thread Message-ID: <20121219115557.GA1809@t510.redhat.com> References: <1355861850-2702-1-git-send-email-lcapitulino@redhat.com> <1355861850-2702-2-git-send-email-lcapitulino@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1355861850-2702-2-git-send-email-lcapitulino@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Luiz Capitulino Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, riel@redhat.com, mst@redhat.com, amit.shah@redhat.com, agl@us.ibm.com On Tue, Dec 18, 2012 at 06:17:29PM -0200, Luiz Capitulino wrote: > Today, the balloon_lock mutex is taken and released by fill_balloon() > and leak_balloon() when both functions are entered and when they > return. > > This commit moves the locking to the caller instead, which is > the balloon() thread. The balloon thread is the sole caller of those > functions today. > > The reason for this move is that the next commit will introduce > a shrinker callback for the balloon driver, which will also call > leak_balloon() but will require different locking semantics. > > Signed-off-by: Luiz Capitulino > --- > drivers/virtio/virtio_balloon.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 2a70558..877e695 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -133,7 +133,6 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num) > /* We can only do one array worth at a time. */ > num = min(num, ARRAY_SIZE(vb->pfns)); > > - mutex_lock(&vb->balloon_lock); > for (vb->num_pfns = 0; vb->num_pfns < num; > vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) { > struct page *page = balloon_page_enqueue(vb_dev_info); > @@ -155,7 +154,6 @@ static void fill_balloon(struct virtio_balloon *vb, size_t num) > /* Did we get any? */ > if (vb->num_pfns != 0) > tell_host(vb, vb->inflate_vq); > - mutex_unlock(&vb->balloon_lock); > } > Since you're removing the locking scheme from within this function, I think it would be a good idea introduce a comment stating its caller must held the mutex vb->balloon_lock. > static void release_pages_by_pfn(const u32 pfns[], unsigned int num) > @@ -177,7 +175,6 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num) > /* We can only do one array worth at a time. */ > num = min(num, ARRAY_SIZE(vb->pfns)); > > - mutex_lock(&vb->balloon_lock); > for (vb->num_pfns = 0; vb->num_pfns < num; > vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) { > page = balloon_page_dequeue(vb_dev_info); > @@ -193,7 +190,6 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num) > * is true, we *have* to do it in this order > */ > tell_host(vb, vb->deflate_vq); > - mutex_unlock(&vb->balloon_lock); > release_pages_by_pfn(vb->pfns, vb->num_pfns); > } > ditto > @@ -306,11 +302,13 @@ static int balloon(void *_vballoon) > || freezing(current)); > if (vb->need_stats_update) > stats_handle_request(vb); > + mutex_lock(&vb->balloon_lock); > if (diff > 0) > fill_balloon(vb, diff); > else if (diff < 0) > leak_balloon(vb, -diff); > update_balloon_size(vb); > + mutex_unlock(&vb->balloon_lock); > } > return 0; > } Just a nitpick: As leak_balloon() is also called at remove_common(), you'll need to introduce the mutex there, similarly. Thanks for move this forward. Cheers! -- Rafael -- 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/ . Don't email: email@kvack.org