On Thu, May 31, 2012 at 03:58:59PM -0700, Hugh Dickins wrote: > On Thu, 31 May 2012, baozich wrote: > > > > > > In their place, mem_cgroup_page_lruvec() to decide the lruvec, > > > previously a side-effect of add, and mem_cgroup_update_lru_size() > > > to maintain the lru_size stats. > > I have a stupid question. I'm not sure whether there is reduplication > > to put both "page" and "zone" parameter in mem_cgroup_page_lruvec(), > > for I noticed that the "struct zone *zone" parameter are usually from > > page_zone(page) in most cases. I think that the semantics of this function > > is to grab the lruvec the page belongs to. So will it be ok if we pass > > only "page" as the parameter, which I think would be cleaner? Please > > fix me if I missed something. > > I share your dislike for passing down an "unnecessary" argument, > but I do think it's justified here. > > If the zone pointer were available simply by page->zone, then yes, > I'd agree with you that it's probably silly to pass zone separately. > > But page_zone(page) is never as trivial as that, and on some memory > layouts it can be a lookup that you'd really prefer to avoid repeating. > > In every(?) case where we're using mem_cgroup_page_lruvec(), the zone > is already known: it's just been used for spin_lock_irq(&zone->lru_lock). > > And when CONFIG_CGROUP_MEM_RES_CTLR is not set, the inline function > mem_cgroup_page_lruvec() uses only zone, not page at all: I wouldn't > want to be slowing down that case with another page_zone(page) lookup. > > Also it's somewhat academic (though not for v3.5), in that this function > goes away in the patches I build upon it; and I expect it also to go away > in the patches Konstantin would build upon it - mem_cgroup_page_lruvec() > is a staging point, before we combine memcg/zone lookup with the locking. > > Hugh I see. Thanks for the detailed explaination. Baozi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>