From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60771) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1chGAx-0005ch-FZ for qemu-devel@nongnu.org; Fri, 24 Feb 2017 08:44:48 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1chGAv-0001fB-9G for qemu-devel@nongnu.org; Fri, 24 Feb 2017 08:44:47 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51036) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1chGAv-0001ep-0c for qemu-devel@nongnu.org; Fri, 24 Feb 2017 08:44:45 -0500 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 231A6C04BD28 for ; Fri, 24 Feb 2017 13:44:45 +0000 (UTC) Date: Fri, 24 Feb 2017 13:44:40 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20170224134440.GE8830@work-vm> References: <20170206173306.20603-1-dgilbert@redhat.com> <20170206173306.20603-6-dgilbert@redhat.com> <87o9xrk9o8.fsf@emacs.mitica> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87o9xrk9o8.fsf@emacs.mitica> Subject: Re: [Qemu-devel] [PATCH v2 05/16] postcopy: enhance ram_block_discard_range for hugepages List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Juan Quintela Cc: qemu-devel@nongnu.org, aarcange@redhat.com * Juan Quintela (quintela@redhat.com) wrote: > "Dr. David Alan Gilbert (git)" wrote: > > From: "Dr. David Alan Gilbert" > > > > Unfortunately madvise DONTNEED doesn't work on hugepagetlb > > so use fallocate(FALLOC_FL_PUNCH_HOLE) > > qemu_fd_getpagesize only sets the page based off a file > > if the file is from hugetlbfs. > > > > Signed-off-by: Dr. David Alan Gilbert > > Reviewed-by: Juan Quintela > > But ... > > > > --- > > exec.c | 13 ++++++++++++- > > 1 file changed, 12 insertions(+), 1 deletion(-) > > > > diff --git a/exec.c b/exec.c > > index e040cdf..c25f6b3 100644 > > --- a/exec.c > > +++ b/exec.c > > @@ -3324,9 +3324,20 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length) > > > > errno = ENOTSUP; /* If we are missing MADVISE etc */ > > > > + if (rb->page_size == qemu_host_page_size) { > > #if defined(CONFIG_MADVISE) > > - ret = qemu_madvise(host_startaddr, length, QEMU_MADV_DONTNEED); > > + ret = qemu_madvise(host_startaddr, length, QEMU_MADV_DONTNEED); > > #endif > > + } else { > > + /* Huge page case - unfortunately it can't do DONTNEED, but > > + * it can do the equivalent by FALLOC_FL_PUNCH_HOLE in the > > + * huge page file. > > + */ > > +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE > > + ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > > + start, length); > > > Why can't we use fallocate() when !CONFIG_MADVISE? > > or even ... > > if (rb->page_size == qemu_host_page_size) { > #if defined(CONFIG_MADVISE) > ret = qemu_madvise(host_startaddr, length, QEMU_MADV_DONTNEED); > #endif > } > > if (ret == -1) { > /* Huge page case - unfortunately it can't do DONTNEED, but > * it can do the equivalent by FALLOC_FL_PUNCH_HOLE in the > * huge page file. > */ > #ifdef CONFIG_FALLOCATE_PUNCH_HOLE > ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > start, length); > #endif > } The fallocate only works where we have an fd, e.g. in the hugepage case; the madvise only works where we have anonymous memory. So if we don't have madvise, we can't use fallocate for normal anonymous memory. Actually, it's much more complicated than that - I've got another patch that adds support for postcopy with memory that's backed by tmpfs with shared=true and that also uses fallocate; I'm trying to decide if it also needs the madvise. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK