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From: "Aneesh Kumar K.V" <>
To: Matthew Wilcox <>,
Cc: Thomas Bogendoerfer <>,
	Vineet Gupta <>,,
	Russell King <>,,,
	Paul Mackerras <>,
	Catalin Marinas <>,,,
	Will Deacon <>,
	"David S. Miller" <>,
Subject: Re: Flushing transparent hugepages
Date: Wed, 09 Sep 2020 15:56:58 +0530	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Matthew Wilcox <> writes:

> PowerPC has special handling of hugetlbfs pages.  Well, that's what
> the config option says, but actually it handles THP as well.  If
> the config option is enabled.
>         if (PageCompound(page)) {
>                 flush_dcache_icache_hugepage(page);
>                 return;
>         }
> #endif

I do have a change posted sometime back to avoid that confusion.

But IIUC we use the head page flags (PG_arch_1) to track whether we need
the flush or not.

> By the way, THPs can be mapped askew -- that is, at an offset which
> means you can't use a PMD to map a PMD sized page.
> Anyway, we don't really have consensus between the various architectures
> on how to handle either THPs or hugetlb pages.  It's not contemplated
> in Documentation/core-api/cachetlb.rst so there's no real surprise
> we've diverged.
> What would you _like_ to see?  Would you rather flush_dcache_page()
> were called once for each subpage, or would you rather maintain
> the page-needs-flushing state once per compound page?  We could also
> introduce flush_dcache_thp() if some architectures would prefer it one
> way and one the other, although that brings into question what to do
> for hugetlbfs pages.
> It might not be a bad idea to centralise the handling of all this stuff
> somewhere.  Sounds like the kind of thing Arnd would like to do ;-) I'll
> settle for getting enough clear feedback about what the various arch
> maintainers want that I can write a documentation update for cachetlb.rst.

      parent reply	other threads:[~2020-09-09 10:28 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-18 15:07 Flushing transparent hugepages Matthew Wilcox
2020-08-18 16:08 ` Will Deacon
2020-08-28 17:06   ` Catalin Marinas
2020-09-09 10:26 ` Aneesh Kumar K.V [this message]

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