From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48294) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1estq3-0004Gx-Ax for qemu-devel@nongnu.org; Mon, 05 Mar 2018 12:23:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1estq0-0002Qn-5w for qemu-devel@nongnu.org; Mon, 05 Mar 2018 12:23:51 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:37296 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 1estpz-0002QZ-VM for qemu-devel@nongnu.org; Mon, 05 Mar 2018 12:23:48 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EB5BC8D6C7 for ; Mon, 5 Mar 2018 17:23:42 +0000 (UTC) Date: Mon, 5 Mar 2018 17:23:24 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20180305172323.GP3131@work-vm> References: <20180216131625.9639-1-dgilbert@redhat.com> <20180216131625.9639-4-dgilbert@redhat.com> <20180228065340.GU18962@xz-mi> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180228065340.GU18962@xz-mi> 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: Peter Xu 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 * Peter Xu (peterx@redhat.com) wrote: > 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. Yes, the problem is you don't get to know until you register it with userfault. > Maybe worth add a comment in the flag definition about this? Yes, I've added: /* Note: Only set at the start of postcopy */ above the qemu_ram_is_uf_zeroable() defintiion; also see the existing '(Set during postcopy)' comment above the #define. > 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 Thanks. Dave > > > > > 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 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK