From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55505) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dUVXZ-00062T-8c for qemu-devel@nongnu.org; Mon, 10 Jul 2017 06:03:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dUVXU-0007mt-Fr for qemu-devel@nongnu.org; Mon, 10 Jul 2017 06:03:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38086) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dUVXU-0007lW-74 for qemu-devel@nongnu.org; Mon, 10 Jul 2017 06:03:36 -0400 Date: Mon, 10 Jul 2017 18:03:23 +0800 From: Peter Xu Message-ID: <20170710100323.GA21344@pxdev.xzpeter.org> References: <20170628190047.26159-1-dgilbert@redhat.com> <20170628190047.26159-3-dgilbert@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170628190047.26159-3-dgilbert@redhat.com> Subject: Re: [Qemu-devel] [RFC 02/29] migrate: Update ram_block_discard_range for shared List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Dr. David Alan Gilbert (git)" Cc: qemu-devel@nongnu.org, a.perevalov@samsung.com, marcandre.lureau@redhat.com, maxime.coquelin@redhat.com, mst@redhat.com, quintela@redhat.com, lvivier@redhat.com, aarcange@redhat.com On Wed, Jun 28, 2017 at 08:00:20PM +0100, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" > > The choice of call to discard a block is getting more complicated > for other cases. We use fallocate PUNCH_HOLE in any file cases; > it works for both hugepage and for tmpfs. > We use the DONTNEED for non-hugepage cases either where they're > anonymous or where they're private. > > Care should be taken when trying other backing files. > > Signed-off-by: Dr. David Alan Gilbert > --- > exec.c | 28 ++++++++++++++++------------ > trace-events | 3 +++ > 2 files changed, 19 insertions(+), 12 deletions(-) > > diff --git a/exec.c b/exec.c > index 69fc5c9b07..4e61226a16 100644 > --- a/exec.c > +++ b/exec.c > @@ -3557,6 +3557,7 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length) > } > > if ((start + length) <= rb->used_length) { > + bool need_madvise, need_fallocate; > uint8_t *host_endaddr = host_startaddr + length; > if ((uintptr_t)host_endaddr & (rb->page_size - 1)) { > error_report("ram_block_discard_range: Unaligned end address: %p", > @@ -3566,23 +3567,26 @@ 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) > - /* Note: We need the madvise MADV_DONTNEED behaviour of definitely > - * freeing the page. > - */ > - ret = madvise(host_startaddr, length, 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. > - */ > + /* The logic here is messy; > + * madvise DONTNEED fails for hugepages > + * fallocate works on hugepages and shmem > + */ > + need_madvise = (rb->page_size == qemu_host_page_size) && > + (rb->fd == -1 || !(rb->flags & RAM_SHARED)); > + need_fallocate = rb->fd != -1; > + if (ret == -1 && need_fallocate) { (ret will always be -1 when reach here?) > #ifdef CONFIG_FALLOCATE_PUNCH_HOLE > ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > start, length); > #endif > } > + if (need_madvise && (!need_fallocate || (ret == 0))) { > +#if defined(CONFIG_MADVISE) > + ret = madvise(host_startaddr, length, MADV_DONTNEED); > +#endif > + } > + trace_ram_block_discard_range(rb->idstr, host_startaddr, > + need_madvise, need_fallocate, ret); How about make the check easier by: if (rb->page_size != qemu_host_page_size || rb->flags & RAM_SHARED) { /* Either huge pages or shared memory will contain rb->fd */ assert(rb->fd); fallocate(rb->fd, ...); } else { madvise(); } Thanks, -- Peter Xu