From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49688) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eqvcm-0007Ci-KY for qemu-devel@nongnu.org; Wed, 28 Feb 2018 01:54:02 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eqvci-0005PC-Ks for qemu-devel@nongnu.org; Wed, 28 Feb 2018 01:54:00 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:56408 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eqvci-0005Oq-Ei for qemu-devel@nongnu.org; Wed, 28 Feb 2018 01:53:56 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D749740FB647 for ; Wed, 28 Feb 2018 06:53:50 +0000 (UTC) Date: Wed, 28 Feb 2018 14:53:40 +0800 From: Peter Xu Message-ID: <20180228065340.GU18962@xz-mi> References: <20180216131625.9639-1-dgilbert@redhat.com> <20180216131625.9639-4-dgilbert@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180216131625.9639-4-dgilbert@redhat.com> Subject: Re: [Qemu-devel] [PATCH v3 03/29] postcopy: use UFFDIO_ZEROPAGE only when available List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Dr. David Alan Gilbert (git)" Cc: qemu-devel@nongnu.org, maxime.coquelin@redhat.com, marcandre.lureau@redhat.com, imammedo@redhat.com, mst@redhat.com, quintela@redhat.com, aarcange@redhat.com On Fri, Feb 16, 2018 at 01:15:59PM +0000, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" > > Use a flag on the RAMBlock to state whether it has the > UFFDIO_ZEROPAGE capability, use it when it's available. > > This allows the use of postcopy on tmpfs as well as hugepage > backed files. > > Signed-off-by: Dr. David Alan Gilbert > --- > exec.c | 15 +++++++++++++++ > include/exec/cpu-common.h | 3 +++ > migration/postcopy-ram.c | 13 ++++++++++--- > 3 files changed, 28 insertions(+), 3 deletions(-) > > diff --git a/exec.c b/exec.c > index 0ec73bc917..1dc15298c2 100644 > --- a/exec.c > +++ b/exec.c > @@ -99,6 +99,11 @@ static MemoryRegion io_mem_unassigned; > */ > #define RAM_RESIZEABLE (1 << 2) > > +/* UFFDIO_ZEROPAGE is available on this RAMBlock to atomically > + * zero the page and wake waiting processes. > + * (Set during postcopy) > + */ > +#define RAM_UF_ZEROPAGE (1 << 3) > #endif > > #ifdef TARGET_PAGE_BITS_VARY > @@ -1767,6 +1772,16 @@ bool qemu_ram_is_shared(RAMBlock *rb) > return rb->flags & RAM_SHARED; > } > > +bool qemu_ram_is_uf_zeroable(RAMBlock *rb) > +{ > + return rb->flags & RAM_UF_ZEROPAGE; > +} > + > +void qemu_ram_set_uf_zeroable(RAMBlock *rb) > +{ > + rb->flags |= RAM_UF_ZEROPAGE; > +} > + > /* Called with iothread lock held. */ > void qemu_ram_set_idstr(RAMBlock *new_block, const char *name, DeviceState *dev) > { > diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h > index 0d861a6289..24d335f95d 100644 > --- a/include/exec/cpu-common.h > +++ b/include/exec/cpu-common.h > @@ -73,6 +73,9 @@ void qemu_ram_set_idstr(RAMBlock *block, const char *name, DeviceState *dev); > void qemu_ram_unset_idstr(RAMBlock *block); > const char *qemu_ram_get_idstr(RAMBlock *rb); > bool qemu_ram_is_shared(RAMBlock *rb); > +bool qemu_ram_is_uf_zeroable(RAMBlock *rb); > +void qemu_ram_set_uf_zeroable(RAMBlock *rb); > + > size_t qemu_ram_pagesize(RAMBlock *block); > size_t qemu_ram_pagesize_largest(void); > > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > index bec6c2c66b..6297979700 100644 > --- a/migration/postcopy-ram.c > +++ b/migration/postcopy-ram.c > @@ -490,6 +490,10 @@ static int ram_block_enable_notify(const char *block_name, void *host_addr, > error_report("%s userfault: Region doesn't support COPY", __func__); > return -1; > } > + if (reg_struct.ioctls & ((__u64)1 << _UFFDIO_ZEROPAGE)) { > + RAMBlock *rb = qemu_ram_block_by_name(block_name); > + qemu_ram_set_uf_zeroable(rb); > + } So the zeroable flag is only set after a listening operation of postcopy migration. One thing I am a bit worried is that if someone else wants to use the flag for a RAMBlock he/she may not notice this. Say, qemu_ram_is_uf_zeroable() is not valid if there is no such an incoming postcopy migration. Maybe worth add a comment in the flag definition about this? Not a big deal (considering that I see no potential QEMU user for userfaultfd in short peroid), so no matter what: Reviewed-by: Peter Xu > > return 0; > } > @@ -699,11 +703,14 @@ int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from, > int postcopy_place_page_zero(MigrationIncomingState *mis, void *host, > RAMBlock *rb) > { > + size_t pagesize = qemu_ram_pagesize(rb); > trace_postcopy_place_page_zero(host); > > - if (qemu_ram_pagesize(rb) == getpagesize()) { > - if (qemu_ufd_copy_ioctl(mis->userfault_fd, host, NULL, getpagesize(), > - rb)) { > + /* Normal RAMBlocks can zero a page using UFFDIO_ZEROPAGE > + * but it's not available for everything (e.g. hugetlbpages) > + */ > + if (qemu_ram_is_uf_zeroable(rb)) { > + if (qemu_ufd_copy_ioctl(mis->userfault_fd, host, NULL, pagesize, rb)) { > int e = errno; > error_report("%s: %s zero host: %p", > __func__, strerror(e), host); > -- > 2.14.3 > -- Peter Xu