Messages in this thread | | | Date | Thu, 27 Jan 2022 01:10:54 +0000 | From | Wei Yang <> | Subject | Re: [PATCH] mm: remove offset check on page->compound_head and folio->lru |
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On Tue, Jan 25, 2022 at 11:11:40AM +0100, Vlastimil Babka wrote: >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? >
If we forget to do it, the compile would fail, right?
Put it here for a future reason is not persuasive.
>>>thus valid pointers are aligned in such a way they can't accidentaly set the >>>bit 0. >>> >>
-- Wei Yang Help you, Help me
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