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Re: [Qemu-devel] [PATCH v3 01/29] migrate: Update ram_block_discard_rang
From: |
Peter Xu |
Subject: |
Re: [Qemu-devel] [PATCH v3 01/29] migrate: Update ram_block_discard_range for shared |
Date: |
Wed, 28 Feb 2018 14:37:01 +0800 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Fri, Feb 16, 2018 at 01:15:57PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> 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 <address@hidden>
> ---
> 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 <address@hidden>
--
Peter Xu
- [Qemu-devel] [PATCH v3 00/29] postcopy+vhost-user/shared ram, Dr. David Alan Gilbert (git), 2018/02/16
- [Qemu-devel] [PATCH v3 01/29] migrate: Update ram_block_discard_range for shared, Dr. David Alan Gilbert (git), 2018/02/16
- Re: [Qemu-devel] [PATCH v3 01/29] migrate: Update ram_block_discard_range for shared,
Peter Xu <=
- [Qemu-devel] [PATCH v3 02/29] qemu_ram_block_host_offset, Dr. David Alan Gilbert (git), 2018/02/16
- [Qemu-devel] [PATCH v3 03/29] postcopy: use UFFDIO_ZEROPAGE only when available, Dr. David Alan Gilbert (git), 2018/02/16
- [Qemu-devel] [PATCH v3 04/29] postcopy: Add notifier chain, Dr. David Alan Gilbert (git), 2018/02/16
- [Qemu-devel] [PATCH v3 05/29] postcopy: Add vhost-user flag for postcopy and check it, Dr. David Alan Gilbert (git), 2018/02/16
- [Qemu-devel] [PATCH v3 08/29] libvhost-user: Open userfaultfd, Dr. David Alan Gilbert (git), 2018/02/16
- [Qemu-devel] [PATCH v3 07/29] libvhost-user: Support sending fds back to qemu, Dr. David Alan Gilbert (git), 2018/02/16
- [Qemu-devel] [PATCH v3 06/29] vhost-user: Add 'VHOST_USER_POSTCOPY_ADVISE' message, Dr. David Alan Gilbert (git), 2018/02/16