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

[Zheng Chuan]

On 2020/8/26 20:30, Dr. David Alan Gilbert wrote:
> * 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.
>>
OK, will take two variables instead to represent base address and length.

>>> +    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 ;-)
>>
OK, i'll try it.

>>> +    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()?
>>
Hi,
I am not sure that because there only one place in qemu to use g_try_renew.
Could you tell me why, because i think g_try_realloc will also return NULL when 
error happen:)

>>> +    }
>>> +    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".
>>
OK, will remove unused initialization in V6.
>> 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.
>>