On 25.07.19 19:38, Alexander Duyck wrote: > On Thu, 2019-07-25 at 18:48 +0200, David Hildenbrand wrote: >> On 25.07.19 17:59, Alexander Duyck wrote: >>> On Thu, Jul 25, 2019 at 1:53 AM David Hildenbrand <david@xxxxxxxxxx> wrote: >>>> On 24.07.19 19:03, Alexander Duyck wrote: >>>>> From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> >>> > > <snip> > >>>> Can't we reuse one of the traditional page flags for that, not used >>>> along with buddy pages? E.g., PG_dirty: Pages that were not hinted yet >>>> are dirty. >>> >>> Reusing something like the dirty bit would just be confusing in my >>> opinion. In addition it looks like Xen has also re-purposed PG_dirty >>> already for another purpose. >> >> You brought up waste page management. A dirty bit for unprocessed pages >> fits perfectly in this context. Regarding XEN, as long as it's not used >> along with buddy pages, no issue. > > I would rather not have to dirty all pages that aren't hinted. That starts > to get too invasive. Ideally we only modify pages if we are hinting on > them. That is why I said I didn't like the use of a dirty bit. What we > want is more of a "guaranteed clean" bit. Not sure if that is too invasive, but fair enough. > >> FWIW, I don't even thing PG_offline matches to what you are using it >> here for. The pages are not logically offline. They were simply buddy >> pages that were hinted. (I'd even prefer a separate page type for that >> instead - if we cannot simply reuse one of the other flags) >> >> "Offline pages" that are not actually offline in the context of the >> buddy is way more confusing. > > Right now offline and hinted are essentially the same thing since the > effect is identical. No they are not the same thing. Regarding virtio-balloon: You are free to reuse any hinted pages immediate. Offline pages (a.k.a. inflated) you might not generally reuse before deflating. > > There may be cases in the future where that is not the case, but with the > current patch set they both result in the pages being evicted from the > guest. > >>> If anything I could probably look at seeing if the PG_private flags >>> are available when a page is in the buddy allocator which I suspect >>> they probably are since the only users I currently see appear to be >>> SLOB and compound pages. Either that or maybe something like PG_head >>> might make sense since once we start allocating them we are popping >>> the head off of the boundary list. >> >> Would also be fine with me. > > Actually I may have found an even better bit if we are going with the > "reporting" name. I could probably use "PG_uptodate" since it looks like > most of its uses are related to filesystems. I will wait till I hear from > Matthew on what bits would be available for use before I update things. Also fine with me. In the optimal case we (in my opinion) a) Don't reuse PG_offline b) Don't use another page type -- Thanks, David / dhildenb
