From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47279) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eqvMe-0004Sy-Lr for qemu-devel@nongnu.org; Wed, 28 Feb 2018 01:37:21 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eqvMZ-0007P3-Hv for qemu-devel@nongnu.org; Wed, 28 Feb 2018 01:37:20 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:49690 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 1eqvMZ-0007Om-CA for qemu-devel@nongnu.org; Wed, 28 Feb 2018 01:37:15 -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 BE579EAEA0 for ; Wed, 28 Feb 2018 06:37:10 +0000 (UTC) Date: Wed, 28 Feb 2018 14:37:01 +0800 From: Peter Xu Message-ID: <20180228063701.GT18962@xz-mi> References: <20180216131625.9639-1-dgilbert@redhat.com> <20180216131625.9639-2-dgilbert@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180216131625.9639-2-dgilbert@redhat.com> Subject: Re: [Qemu-devel] [PATCH v3 01/29] 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, 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 01:15:57PM +0000, 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 | 60 ++++++++++++++++++++++++++++++++++++++++++++++-------------- > trace-events | 3 ++- > 2 files changed, 48 insertions(+), 15 deletions(-) > > diff --git a/exec.c b/exec.c > index e8d7b335b6..b1bb477776 100644 > --- a/exec.c > +++ b/exec.c > @@ -3702,6 +3702,7 @@ 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", > @@ -3711,29 +3712,60 @@ 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); > + need_fallocate = rb->fd != -1; > + if (need_fallocate) { > + /* For a file, this causes the area of the file to be zero'd > + * if read, and for hugetlbfs also causes it to be unmapped > + * so a userfault will trigger. > */ > #ifdef CONFIG_FALLOCATE_PUNCH_HOLE > ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > start, length); > + if (ret) { > + ret = -errno; > + error_report("ram_block_discard_range: Failed to fallocate " > + "%s:%" PRIx64 " +%zx (%d)", > + rb->idstr, start, length, ret); > + goto err; > + } > +#else > + ret = -ENOSYS; > + error_report("ram_block_discard_range: fallocate not available/file" > + "%s:%" PRIx64 " +%zx (%d)", > + rb->idstr, start, length, ret); > + goto err; > #endif > } > - if (ret) { > - ret = -errno; > - error_report("ram_block_discard_range: Failed to discard range " > + if (need_madvise) { > + /* For normal RAM this causes it to be unmapped, > + * for shared memory it causes the local mapping to disappear > + * and to fall back on the file contents (which we just > + * fallocate'd away). > + */ > +#if defined(CONFIG_MADVISE) > + ret = madvise(host_startaddr, length, MADV_DONTNEED); > + if (ret) { > + ret = -errno; > + error_report("ram_block_discard_range: Failed to discard range " > + "%s:%" PRIx64 " +%zx (%d)", > + rb->idstr, start, length, ret); > + goto err; > + } > +#else > + ret = -ENOSYS; > + error_report("ram_block_discard_range: MADVISE not available" > "%s:%" PRIx64 " +%zx (%d)", > rb->idstr, start, length, ret); > + goto err; > +#endif > } > + trace_ram_block_discard_range(rb->idstr, host_startaddr, > + need_madvise, need_fallocate, ret); Nit: worth to log the length too if it's named as "range"? Either with/without: Reviewed-by: Peter Xu -- Peter Xu