Messages in this thread | | | Date | Tue, 25 Jan 2022 11:11:40 +0100 | Subject | Re: [PATCH] mm: remove offset check on page->compound_head and folio->lru | From | Vlastimil Babka <> |
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On 1/24/22 23:55, Wei Yang wrote: > On Mon, Jan 24, 2022 at 11:30:10AM +0100, Vlastimil Babka wrote: >>On 1/23/22 02:38, Wei Yang wrote: >>> On Sat, Jan 08, 2022 at 08:13:40AM +0000, Wei Yang wrote: >>>>On Sat, Jan 08, 2022 at 12:49:53AM +0000, Matthew Wilcox wrote: >>>>>On Fri, Jan 07, 2022 at 04:08:25PM -0800, Andrew Morton wrote: >>>> >>>>To me, if folio has the same layout of page, folio meets this requirement. I >>>>still not catch the point why we need this check here. >>>> >>> >>> Hi, Matthew >>> >>> Are you back from vocation? If you could give more insight on this check, I >>> would be appreciated. >> >>I can offer my insight (which might be of course wrong). Ideally one day >>page.lru will be gone and only folio will be used for LRU pages. Then there >>won't be a FOLIO_MATCH(lru, lru); and FOLIO_MATCH(compound_head, lru); >>won't appear to be redundant anymore. lru is list_head so two pointers and > > Thanks for your comment. > > I can't imagine the final result. If we would remove page.lru, we could remove > FOLIO_MATCH(lru, lru) and add FOLIO_MATCH(compound_head, lru) at that moment?
Yes, or we could forget to do it. Adding it right now is another option that Matthew has chosen and I don't see a strong reason to change it. Can you measure a kernel build speedup thanks to removing the now redundant check?
>>thus valid pointers are aligned in such a way they can't accidentaly set the >>bit 0. >> >
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