From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55879) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dmZ6g-00031f-CH for qemu-devel@nongnu.org; Tue, 29 Aug 2017 01:30:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dmZ6b-0006v5-7L for qemu-devel@nongnu.org; Tue, 29 Aug 2017 01:30:34 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53420) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dmZ6a-0006uB-Tx for qemu-devel@nongnu.org; Tue, 29 Aug 2017 01:30:29 -0400 Date: Tue, 29 Aug 2017 13:30:11 +0800 From: Peter Xu Message-ID: <20170829053011.GS14174@pxdev.xzpeter.org> References: <20170824192730.8440-1-dgilbert@redhat.com> <20170824192730.8440-4-dgilbert@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170824192730.8440-4-dgilbert@redhat.com> Subject: Re: [Qemu-devel] [RFC v2 03/32] 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, a.perevalov@samsung.com, mst@redhat.com, marcandre.lureau@redhat.com, quintela@redhat.com, lvivier@redhat.com, aarcange@redhat.com, felipe@nutanix.com On Thu, Aug 24, 2017 at 08:27:01PM +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 | 35 ++++++++++++++++++++++++----------- > trace-events | 3 +++ > 2 files changed, 27 insertions(+), 11 deletions(-) > > diff --git a/exec.c b/exec.c > index d20c34ca83..67df2909ce 100644 > --- a/exec.c > +++ b/exec.c > @@ -3573,6 +3573,7 @@ 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", > @@ -3582,23 +3583,35 @@ 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); > #endif > } > + /* i.e. need madvise but skip it if the fallocate failed */ > + if (need_madvise && (!need_fallocate || (ret == 0))) { I'll slightly prefer: trace_ram_block_discard_range(); if (need_fallocate) { ret = fallocate(); if (ret) { error_report(); goto err; } } if (need_madvise) { ret = madvise(); if (ret) { error_report(); goto err; } } But it is personal preference. For either way: Reviewed-by: Peter Xu > + /* 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); > +#endif > + } > + trace_ram_block_discard_range(rb->idstr, host_startaddr, > + need_madvise, need_fallocate, ret); > if (ret) { > ret = -errno; > error_report("ram_block_discard_range: Failed to discard range " > diff --git a/trace-events b/trace-events > index 1f50f56d9d..213ee34f89 100644 > --- a/trace-events > +++ b/trace-events > @@ -55,6 +55,9 @@ dma_complete(void *dbs, int ret, void *cb) "dbs=%p ret=%d cb=%p" > dma_blk_cb(void *dbs, int ret) "dbs=%p ret=%d" > dma_map_wait(void *dbs) "dbs=%p" > > +# exec.c > +ram_block_discard_range(const char *rbname, void *hva, bool need_madvise, bool need_fallocate, int ret) "%s@%p: madvise: %d fallocate: %d ret: %d" > + > # memory.c > memory_region_ops_read(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size) "cpu %d mr %p addr 0x%"PRIx64" value 0x%"PRIx64" size %u" > memory_region_ops_write(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size) "cpu %d mr %p addr 0x%"PRIx64" value 0x%"PRIx64" size %u" > -- > 2.13.5 > -- Peter Xu