Re: [PATCH] mm: vmscan: correct nr_reclaimed for THP

From: Yang Shi
Date: Fri May 10 2019 - 12:51:37 EST

On 5/10/19 9:36 AM, Matthew Wilcox wrote:
On Fri, May 10, 2019 at 10:12:40AM +0800, Huang, Ying wrote:
+ nr_reclaimed += (1 << compound_order(page));
How about to change this to

nr_reclaimed += hpage_nr_pages(page);
Please don't. That embeds the knowledge that we can only swap out either
normal pages or THP sized pages. I'm trying to make the VM capable of
supporting arbitrary-order pages, and this would be just one more place
to fix.

I'm sympathetic to the "self documenting" argument. My current tree has
a patch in it:

mm: Introduce compound_nr
Replace 1 << compound_order(page) with compound_nr(page). Minor
improvements in readability.

It goes along with this patch:

mm: Introduce page_size()

It's unnecessarily hard to find out the size of a potentially huge page.
Replace 'PAGE_SIZE << compound_order(page)' with page_size(page).

So you prefer keeping using "1 << compound_order" as v1 did? Then you will convert all "1 << compound_order" to compound_nr?

Better suggestions on naming gratefully received. I'm more happy with
page_size() than I am with compound_nr(). page_nr() gives the wrong
impression; page_count() isn't great either.