On 05/19/2015 05:55 AM, Kirill A. Shutemov wrote:
+ if (compound_mapcount(page))
+ ret += compound_mapcount(page) - 1;
This looks like it could uselessly duplicate-inline the code for
compound_mapcount(). It has atomics and smp_rmb() so I'm not sure if the
compiler can just "squash it".
Good point. I'll rework this.
Hm BTW I think same duplication of compound_head() happens in
lock_page(), where it's done by trylock_page() and then __lock_page(),
which is also in different compilation unit to make things worse.
I can imagine it's solvable by introducing variants of __lock_page* that
expect to be already given a head page... if it's worth the trouble.
On the other hand, a simple atomic read that was page_mapcount() has turned
into multiple atomic reads and flag checks. What about the stability of the
whole result? Are all callers ok? (maybe a later page deals with it).
Urghh.. I'll look into this.
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