On Thu, Apr 08, 2021 at 01:40:33PM -0700, Yang Shi wrote:
> Thanks a lot for the example code. You didn't miss anything. At first
> glance, I thought your suggestion seemed neater. Actually I
> misunderstood what Dave said about "That could really have caused some
> interesting problems." with multiple calls to migrate_pages(). I was
> thinking about:
>
> unsigned long foo()
> {
> unsigned long *ret_succeeded;
>
> migrate_pages(..., ret_succeeded);
>
> migrate_pages(..., ret_succeeded);
>
> return *ret_succeeded;
> }
But that would not be a problem as well. I mean I am not sure what is
foo() supposed to do.
I assume is supposed to return the *total* number of pages that were
migrated?
Then could do something like:
unsigned long foo()
{
unsigned long ret_succeeded;
unsigned long total_succeeded = 0;
migrate_pages(..., &ret_succeeded);
total_succeeded += ret_succeeded;
migrate_pages(..., &ret_succeeded);
total_succeeded += ret_succeeded;
return *total_succeeded;
}
But AFAICS, you would have to do that with Wei Xu's version and with
mine, no difference there.
IIUC, Dave's concern was that nr_succeeded was only set to 0 at the beginning
of the function, and never reset back, which means, we would carry the
sum of previous nr_succeeded instead of the nr_succeeded in that round.
That would be misleading for e.g: reclaim in case we were to call
migrate_pages() several times, as instead of a delta value, nr_succeeded
would accumulate.
But that won't happen neither with Wei Xu's version nor with mine.
--
Oscar Salvador
SUSE L3
