Messages in this thread | | | Date | Sat, 8 Jan 2022 08:13:40 +0000 | From | Wei Yang <> | Subject | Re: [PATCH] mm: remove offset check on page->compound_head and folio->lru |
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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: >> On Fri, 7 Jan 2022 22:11:20 +0000 Matthew Wilcox <willy@infradead.org> wrote: >> >> > > Hi, Matthew >> > > >> > > Would you mind sharing some insight on this check? >> > >> > It's right there in the comments. >> >> Well I can't figure out which comment you're referring to? > > * WARNING: bit 0 of the first word is used for PageTail(). That > * means the other users of this union MUST NOT use the bit to > * avoid collision and false-positive PageTail(). >
I know this requirement on bit 0 of first word. But I don't see the connection between this and the check of page->compound_head and folio->lru.
This is more like a internal requirement on struct page. There are 8 struct in this five words union. And this requirement apply to bit 0 of first word of all those five struct.
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.
-- Wei Yang Help you, Help me
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