[CRIU] [PATCH 1/3] page-pipe: allow to handle pipes in batch mode

[Pavel Emelyanov]

On 01/30/2014 12:21 PM, Andrey Wagin wrote:
> 2014-01-30 Pavel Emelyanov <xemul at parallels.com>:
>> On 01/30/2014 12:12 AM, Andrew Vagin wrote:
>>> On Wed, Jan 29, 2014 at 05:13:23PM +0400, Pavel Emelyanov wrote:
>>>> On 01/27/2014 06:22 PM, Andrey Vagin wrote:
>>>>> The problem is that vmsplice() to a big pipe fails very often.
>>>>>
>>>>> The kernel allocates the linear chunk of memory for pipe buffer
>>>>> descriptos, but big allocation in kernel can fail.
>>>>>
>>>>> So we need to restrict maximal capacity of pipes. But the number of
>>>>> pipes is restricted too, so we need to dump memory in a batch mode.
>>>>
>>>> Batch mode means "several at once". Do you mean "... using one pipe"?
>>>
>>> I mean match mode "several at once" ;).
>>
>> Then current mode is batch also -- it pulls several pages into several
>> pipes and dumps them all at once.
> 
> The current mode does one iteration per process. The number of pipes
> is not limited.
> 
> Pavel, pls look at the next patch, it starts to use this code.

I did. Let's try to follow the code with patches applied.

__parasite_dump_pages_seized();
 `- create_page_pipe();
 |    `- pp = xmalloc();
 |         `- pp->pipe_nr = INT_MAX;
 |            /* WTF? pp->nr_pipes initialization is removed */
 |            page_pipe_grow();
 |              `- pp->nr_pipes++; /* FTW? Why nr_pipes contains a garbage? */
 |                 open_pipe();
 |                   `- pp->pipe_nr--; /* For the record. INT_MAX - 1 is now here. */
 `- page_pipe_start_batching();
 |   `- pp->pipe_nr = NR_PIPES_PER_BATCH; /* FTF? INT_MAX - 1 doesn't matter any longer?
 |                                           Any why it's NR_..._BATCH, while there's the whole 1 pipe in there? */
 `- generate_iovs()
     `- page_pipe_add_page()
         `- if (pp->pipe_nr == 0)
         |    `- pp->batch_cb();
         |       page_pipe_cleanup();        /* WTF? The pre-dump's pages get all flushed! */
         |         `- page_pipe_close_buf(); /* WTF? Why do we start from the very beginning, there's
         |                                      NR_..._BATCH plus 1 pipe in there already. */
         |
         `- page_pipe_grow();
             `- pp->nr_pipes++; /* WTF? This is increase-only counter. */

I'm afraid that the WTF-per-KLOC value is too high to apply this set.

Thanks,
Pavel