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

[Dr. David Alan Gilbert]

* David Edmondson (dme@dme.org) wrote:
> On Monday, 2020-08-24 at 17:14:34 +08, Chuan Zheng 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;
> 
> There's no need for an iovec now that crc32() is being used.
> 
> > +    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;
> 
> There's no need to initialise "ret".
> 
> > +    GRand *rand = g_rand_new();
> 
> Calling g_rand_new() when the result may not be used (because of the
> various conditions immediately below) seems as though it might waste
> entropy. Could this be pushed down just above the loop? It would even
> get rid of the gotos ;-)
> 
> > +    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;
> 
> Doing the calculation this way around seems odd. Why was it not:
> 
>     info->sample_pages_count = (qemu_ram_get_used_length(block) >>
>                                 DIRTYRATE_PAGE_SHIFT_GB) *
>                                 sample_pages_per_gigabytes;
> 
> ?

Because that would give 0 for a 0.5GB block

Dave

> > +
> > +    /* 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));
> 
> g_try_renew() instead of g_try_realloc()?
> 
> > +    }
> > +    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;
> 
> There's no need to initialise "info" or "block".
> 
> The declaration of "info" could be pushed into the loop.
> 
> > +    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 9db269d..5050add 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
> > +
> >  /* Take 1s as default for calculation duration */
> >  #define DEFAULT_FETCH_DIRTYRATE_TIME_SEC          1
> >  
> > -- 
> > 1.8.3.1
> 
> dme.
> -- 
> You bring light in.
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK