Re: [PATCH] mm: batch-free pcp list if possible

On Thu, 10 Feb 2011 09:35:44 +0000
Mel Gorman [off-list ref] wrote:

quoted

What's the point in that?  What relationship does the number of
contiguous empty lists have with the number of pages to free from one
list?

The point is to avoid excessive checking of empty lists.

It seems pretty simple to me to skip the testing of empty lists
altogether.  I suggested one way, however I suspect a better approach
might be to maintain a count of the number of pages in each list and
then change free_pcppages_bulk() so that it calculates up-front the
number of pages to free from each list (equal proportion of each) then
sits in a tight loop freeing that number of pages.

It might be that the overhead of maintaining the per-list count makes
that not worthwhile.  It'll be hard to tell because the count
maintenance cost will be smeared all over the place.

I doubt if any of it matters much, compared to the cost of allocating,
populating and freeing a page.  I just want free_pcppages_bulk() to
stop hurting my brain ;)


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