Re: [PATCH v5 06/12] migration/dirtyrate: Record hash results for each sampled page

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Zheng Chuan (zhengchuan@huawei.com) wrote:
> 
> 
> On 2020/8/26 20:35, Dr. David Alan Gilbert wrote:
> > * Chuan Zheng (zhengchuan@huawei.com) wrote:
> >> Record hash results for each sampled page, crc32 is taken to calculate
> >> hash results for each sampled 4K-page.
> >>
> >> Signed-off-by: Chuan Zheng <zhengchuan@huawei.com>
> >> Signed-off-by: YanYing Zhuang <ann.zhuangyanying@huawei.com>
> >> ---
> >>  migration/dirtyrate.c | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >>  migration/dirtyrate.h |  15 ++++++
> >>  2 files changed, 151 insertions(+)
> >>
> >> diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c
> >> index f6a94d8..66de426 100644
> >> --- a/migration/dirtyrate.c
> >> +++ b/migration/dirtyrate.c
> >> @@ -10,6 +10,7 @@
> >>   * See the COPYING file in the top-level directory.
> >>   */
> >>  
> >> +#include <zlib.h>
> >>  #include "qemu/osdep.h"
> >>  #include "qapi/error.h"
> >>  #include "crypto/hash.h"
> >> @@ -66,6 +67,141 @@ static void update_dirtyrate(uint64_t msec)
> >>      DirtyStat.dirty_rate = dirtyrate;
> >>  }
> >>  
> >> +/*
> >> + * get hash result for the sampled memory with length of 4K byte in ramblock,
> >> + * which starts from ramblock base address.
> >> + */
> >> +static uint32_t get_ramblock_vfn_hash(struct RamblockDirtyInfo *info,
> >> +                                      uint64_t vfn)
> >> +{
> >> +    struct iovec iov_array;
> >> +    uint32_t crc;
> >> +
> >> +    iov_array.iov_base = info->ramblock_addr +
> >> +                         vfn * DIRTYRATE_SAMPLE_PAGE_SIZE;
> >> +    iov_array.iov_len = DIRTYRATE_SAMPLE_PAGE_SIZE;
> >> +
> >> +    crc = crc32(0, iov_array.iov_base, iov_array.iov_len);
> >> +
> >> +    return crc;
> >> +}
> >> +
> >> +static int save_ramblock_hash(struct RamblockDirtyInfo *info)
> >> +{
> >> +    unsigned int sample_pages_count;
> >> +    int i;
> >> +    int ret = -1;
> >> +    GRand *rand = g_rand_new();
> >> +
> >> +    sample_pages_count = info->sample_pages_count;
> >> +
> >> +    /* ramblock size less than one page, return success to skip this ramblock */
> >> +    if (unlikely(info->ramblock_pages == 0 || sample_pages_count == 0)) {
> >> +        ret = 0;
> >> +        goto out;
> >> +    }
> >> +
> >> +    info->hash_result = g_try_malloc0_n(sample_pages_count,
> >> +                                        sizeof(uint32_t));
> >> +    if (!info->hash_result) {
> >> +        ret = -1;
> >> +        goto out;
> >> +    }
> >> +
> >> +    info->sample_page_vfn = g_try_malloc0_n(sample_pages_count,
> >> +                                            sizeof(uint64_t));
> >> +    if (!info->sample_page_vfn) {
> >> +        g_free(info->hash_result);
> >> +        ret = -1;
> >> +        goto out;
> >> +    }
> >> +
> >> +    for (i = 0; i < sample_pages_count; i++) {
> >> +        info->sample_page_vfn[i] = g_rand_int_range(rand, 0,
> >> +                                                    info->ramblock_pages - 1);
> >> +        info->hash_result[i] = get_ramblock_vfn_hash(info,
> >> +                                                     info->sample_page_vfn[i]);
> >> +    }
> >> +    ret = 0;
> >> +
> >> +out:
> >> +    g_rand_free(rand);
> >> +    return ret;
> >> +}
> >> +
> >> +static void get_ramblock_dirty_info(RAMBlock *block,
> >> +                                    struct RamblockDirtyInfo *info,
> >> +                                    struct DirtyRateConfig *config)
> >> +{
> >> +    uint64_t sample_pages_per_gigabytes = config->sample_pages_per_gigabytes;
> >> +
> >> +    /* Right shift 30 bits to calc block size in GB */
> >> +    info->sample_pages_count = (qemu_ram_get_used_length(block) *
> >> +                                sample_pages_per_gigabytes) >>
> >> +                                DIRTYRATE_PAGE_SHIFT_GB;
> >> +
> >> +    /* Right shift 12 bits to calc page count in 4KB */
> >> +    info->ramblock_pages = qemu_ram_get_used_length(block) >>
> >> +                           DIRTYRATE_PAGE_SHIFT_KB;
> >> +    info->ramblock_addr = qemu_ram_get_host_addr(block);
> >> +    strcpy(info->idstr, qemu_ram_get_idstr(block));
> >> +}
> >> +
> >> +static struct RamblockDirtyInfo *
> >> +alloc_ramblock_dirty_info(int *block_index,
> >> +                          struct RamblockDirtyInfo *block_dinfo)
> >> +{
> >> +    struct RamblockDirtyInfo *info = NULL;
> >> +    int index = *block_index;
> >> +
> >> +    if (!block_dinfo) {
> >> +        index = 0;
> >> +        block_dinfo = g_try_new(struct RamblockDirtyInfo, 1);
> >> +    } else {
> >> +        index++;
> >> +        block_dinfo = g_try_realloc(block_dinfo, (index + 1) *
> >> +                                    sizeof(struct RamblockDirtyInfo));
> >> +    }
> >> +    if (!block_dinfo) {
> >> +        return NULL;
> >> +    }
> >> +
> >> +    info = &block_dinfo[index];
> >> +    *block_index = index;
> >> +    memset(info, 0, sizeof(struct RamblockDirtyInfo));
> >> +
> >> +    return block_dinfo;
> >> +}
> >> +
> >> +static int record_ramblock_hash_info(struct RamblockDirtyInfo **block_dinfo,
> >> +                                     struct DirtyRateConfig config,
> >> +                                     int *block_index)
> >> +{
> >> +    struct RamblockDirtyInfo *info = NULL;
> >> +    struct RamblockDirtyInfo *dinfo = NULL;
> >> +    RAMBlock *block = NULL;
> >> +    int index = 0;
> >> +
> >> +    RAMBLOCK_FOREACH_MIGRATABLE(block) {
> >> +        dinfo = alloc_ramblock_dirty_info(&index, dinfo);
> >> +        if (dinfo == NULL) {
> >> +            return -1;
> >> +        }
> >> +        info = &dinfo[index];
> >> +        get_ramblock_dirty_info(block, info, &config);
> >> +        if (save_ramblock_hash(info) < 0) {
> >> +            *block_dinfo = dinfo;
> >> +            *block_index = index;
> >> +            return -1;
> >> +        }
> >> +    }
> >> +
> >> +    *block_dinfo = dinfo;
> >> +    *block_index = index;
> >> +
> >> +    return 0;
> >> +}
> >> +
> >>  static void calculate_dirtyrate(struct DirtyRateConfig config)
> >>  {
> >>      /* todo */
> >> diff --git a/migration/dirtyrate.h b/migration/dirtyrate.h
> >> index 8e25d93..e3adead 100644
> >> --- a/migration/dirtyrate.h
> >> +++ b/migration/dirtyrate.h
> >> @@ -24,6 +24,21 @@
> >>   */
> >>  #define RAMBLOCK_INFO_MAX_LEN                     256
> >>  
> >> +/*
> >> + * Sample page size 4K as default.
> >> + */
> >> +#define DIRTYRATE_SAMPLE_PAGE_SIZE                4096
> >> +
> >> +/*
> >> + * Sample page size 4K shift
> >> + */
> >> +#define DIRTYRATE_PAGE_SHIFT_KB                   12
> >> +
> >> +/*
> >> + * Sample page size 1G shift
> >> + */
> >> +#define DIRTYRATE_PAGE_SHIFT_GB                   30
> > 
> > Your naming is really odd here;  'PAGE_SHIFT_KB' divides
> > by 4KB, where as 'PAGE_SHIFT_GB' divices by 1KB.
> > 
> > Simplify this;  you can just do >>30 for GB because it's well known;
> > you don't need a #define constant for simple KB,MB,GB since
> > we all know them.
> > 
> Hi, Dave.
> Thank you for review.
> OK, i will fix that in V6:)
> > Also, I've asked before - do you really want 4KB explicitly - or
> > should you just use TARGET_PAGE_SIZE and TARGET_PAGE_BITS ?
> > 
> > Dave
> >
> TARGET_PAGE_SIZE will be 2M or 1G for HugePage.
> As you see, what we get is hash result of every 'virtual' 4K-page.
> We care about if it is dirty within 4K length in ramblock, which would be more
> accurate than TARGET_PAGE_SIZE which could be 2M or 1G.
> On the other hand, the hugepage will be broken up into 4K during migration.
> 
> I think it is better we do hash at 'virtual' 4K-page granularity.

TARGET_PAGE_SIZE is never 2M or 1G; it's always based on the smallest
MMU page on the platform; on x86 it's always 4kB; it's the unit that the
migration code works in when dealing with pages.
(use TARGET_PAGE_BITS to shift by).

Dave

> >> +
> >>  /* Take 1s as default for calculation duration */
> >>  #define DEFAULT_FETCH_DIRTYRATE_TIME_SEC          1
> >>  
> >> -- 
> >> 1.8.3.1
> >>
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK