Re: [Xen-devel] [PATCH 6 of 9] xenpaging: add evict_pages function

[George Dunlap <dunlapg@xxxxxxxxx>]

On Thu, Sep 15, 2011 at 9:16 AM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> On Thu, 2011-09-15 at 02:16 -0400, Olaf Hering wrote:
>> # HG changeset patch
>> # User Olaf Hering <olaf@xxxxxxxxx>
>> # Date 1316067230 -7200
>> # Node ID 3a3a5979b799d948802183d10d65894ee84a872f
>> # Parent  6beca8cbc2c92900859712f8738db17084bcebdb
>> xenpaging: add evict_pages function
>>
>> Add new function to evict a couple of pages.
>
> Do you really mean "a couple" here? (that generally means exactly two).

LIterally "couple" means two, but at least in US idiom, "a couple of
[foo]" means a small indeterminate number, usually 2-4.

In any case, a more precise description seems like a better idea -- it
looks like it takes an argument for the number of pages to evict; and
it's not adding a new function, it's pulling existing code into a
function.  So, "Pull eviction loop into a function" would probably be
a better description.

 -George

> >From the implementation I think you mean evict a batch of pages?
>
>> Allocate all possible slots in a paging file to allow growing and
>> shrinking of the number of paged-out pages. Adjust other places to
>> iterate over all slots.
>>
>> This change is required by subsequent patches.
>>
>> Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
>>
>> diff -r 6beca8cbc2c9 -r 3a3a5979b799 tools/xenpaging/xenpaging.c
>> --- a/tools/xenpaging/xenpaging.c
>> +++ b/tools/xenpaging/xenpaging.c
>> @@ -597,6 +597,30 @@ static int evict_victim(xenpaging_t *pag
>>      return ret;
>>  }
>>
>> +/* Evict a couple of pages and write them to a free slot in the paging file 
>> */
>> +static int evict_pages(xenpaging_t *paging, int fd, xenpaging_victim_t 
>> *victims, int num_pages)
>> +{
>> +    xc_interface *xch = paging->xc_handle;
>> +    int rc, slot, num = 0;
>> +
>> +    for ( slot = 0; slot < paging->max_pages && num < num_pages; slot++ )
>> +    {
>> +        /* Slot is allocated */
>> +        if ( victims[slot].gfn != INVALID_MFN )
>> +            continue;
>> +
>> +        rc = evict_victim(paging, &victims[slot], fd, slot);
>> +        if ( rc == -ENOSPC )
>> +            break;
>> +        if ( rc == -EINTR )
>> +            break;
>> +        if ( num && num % 100 == 0 )
>> +            DPRINTF("%d pages evicted\n", num);
>> +        num++;
>> +    }
>> +    return num;
>> +}
>> +
>>  int main(int argc, char *argv[])
>>  {
>>      struct sigaction act;
>> @@ -639,7 +663,12 @@ int main(int argc, char *argv[])
>>          return 2;
>>      }
>>
>> -    victims = calloc(paging->num_pages, sizeof(xenpaging_victim_t));
>> +    /* Allocate upper limit of pages to allow growing and shrinking */
>> +    victims = calloc(paging->max_pages, sizeof(xenpaging_victim_t));
>> +
>> +    /* Mark all slots as unallocated */
>> +    for ( i = 0; i < paging->max_pages; i++ )
>> +        victims[i].gfn = INVALID_MFN;
>>
>>      /* ensure that if we get a signal, we'll do cleanup, then exit */
>>      act.sa_handler = close_handler;
>> @@ -653,18 +682,7 @@ int main(int argc, char *argv[])
>>      /* listen for page-in events to stop pager */
>>      create_page_in_thread(paging);
>>
>> -    /* Evict pages */
>> -    for ( i = 0; i < paging->num_pages; i++ )
>> -    {
>> -        rc = evict_victim(paging, &victims[i], fd, i);
>> -        if ( rc == -ENOSPC )
>> -            break;
>> -        if ( rc == -EINTR )
>> -            break;
>> -        if ( i % 100 == 0 )
>> -            DPRINTF("%d pages evicted\n", i);
>> -    }
>> -
>> +    i = evict_pages(paging, fd, victims, paging->num_pages);
>>      DPRINTF("%d pages evicted. Done.\n", i);
>>
>>      /* Swap pages in and out */
>> @@ -690,13 +708,13 @@ int main(int argc, char *argv[])
>>              if ( test_and_clear_bit(req.gfn, paging->bitmap) )
>>              {
>>                  /* Find where in the paging file to read from */
>> -                for ( i = 0; i < paging->num_pages; i++ )
>> +                for ( i = 0; i < paging->max_pages; i++ )
>>                  {
>>                      if ( victims[i].gfn == req.gfn )
>>                          break;
>>                  }
>>
>> -                if ( i >= paging->num_pages )
>> +                if ( i >= paging->max_pages )
>>                  {
>>                      DPRINTF("Couldn't find page %"PRIx64"\n", req.gfn);
>>                      goto out;
>>
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>> http://lists.xensource.com/xen-devel
>
>
>
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