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Re: [Qemu-devel] [PATCH v2 09/16] postcopy: Use temporary for placing ze
From: |
Laurent Vivier |
Subject: |
Re: [Qemu-devel] [PATCH v2 09/16] postcopy: Use temporary for placing zero huge pages |
Date: |
Fri, 24 Feb 2017 16:31:44 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 |
On 06/02/2017 18:32, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> The kernel can't do UFFDIO_ZEROPAGE for huge pages, so we have
> to allocate a temporary (always zero) page and use UFFDIO_COPYPAGE
> on it.
>
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> Reviewed-by: Juan Quintela <address@hidden>
> ---
> include/migration/migration.h | 1 +
> migration/postcopy-ram.c | 23 +++++++++++++++++++++--
> 2 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index c9c1d5f..bd399fc 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -108,6 +108,7 @@ struct MigrationIncomingState {
> QEMUFile *to_src_file;
> QemuMutex rp_mutex; /* We send replies from multiple threads */
> void *postcopy_tmp_page;
> + void *postcopy_tmp_zero_page;
>
> QEMUBH *bh;
>
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index a8b7fed..4c736d2 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -324,6 +324,10 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState
> *mis)
> munmap(mis->postcopy_tmp_page, mis->largest_page_size);
> mis->postcopy_tmp_page = NULL;
> }
> + if (mis->postcopy_tmp_zero_page) {
> + munmap(mis->postcopy_tmp_zero_page, mis->largest_page_size);
> + mis->postcopy_tmp_zero_page = NULL;
> + }
> trace_postcopy_ram_incoming_cleanup_exit();
> return 0;
> }
> @@ -593,8 +597,23 @@ int postcopy_place_page_zero(MigrationIncomingState
> *mis, void *host,
> return -e;
> }
> } else {
> - /* TODO: The kernel can't use UFFDIO_ZEROPAGE for hugepages */
> - assert(0);
> + /* The kernel can't use UFFDIO_ZEROPAGE for hugepages */
> + if (!mis->postcopy_tmp_zero_page) {
> + mis->postcopy_tmp_zero_page = mmap(NULL, mis->largest_page_size,
> + PROT_READ | PROT_WRITE,
> + MAP_PRIVATE | MAP_ANONYMOUS,
> + -1, 0);
> + if (mis->postcopy_tmp_zero_page == MAP_FAILED) {
> + int e = errno;
> + mis->postcopy_tmp_zero_page = NULL;
> + error_report("%s: %s mapping large zero page",
> + __func__, strerror(e));
> + return -e;
> + }
> + memset(mis->postcopy_tmp_zero_page, '\0',
> mis->largest_page_size);
> + }
> + return postcopy_place_page(mis, host, mis->postcopy_tmp_zero_page,
> + pagesize);
> }
It's sad to have to allocate 1 huge page just to zero them.
Are you sure the kernel doesn't support UFFDIO_ZEROPAGE for huge page.
It seems __mcopy_atomic() manages HUGETLB vma (it is called by
mfill_zeropage(), called by userfaultfd_zeropage())?
Anyway, the code looks good:
Reviewed-by: Laurent Vivier <address@hidden>
[Qemu-devel] [PATCH v2 07/16] postcopy: Record largest page size, Dr. David Alan Gilbert (git), 2017/02/06