From: "Aneesh Kumar K.V" <aneesh.kumar@linux•ibm.com>
To: Matthew Wilcox <willy@infradead•org>, linux-arch@vger•kernel.org
Cc: Thomas Bogendoerfer <tsbogend@alpha•franken.de>,
Will Deacon <will@kernel•org>, Vineet Gupta <vgupta@synopsys•com>,
Russell King <linux@armlinux•org.uk>,
linux-mips@vger•kernel.org, linux-mm@kvack•org,
Paul Mackerras <paulus@samba•org>,
Catalin Marinas <catalin.marinas@arm•com>,
sparclinux@vger•kernel.org, linux-snps-arc@lists•infradead.org,
linuxppc-dev@lists•ozlabs.org,
"David S. Miller" <davem@davemloft•net>,
linux-arm-kernel@lists•infradead.org
Subject: Re: Flushing transparent hugepages
Date: Wed, 09 Sep 2020 15:56:58 +0530 [thread overview]
Message-ID: <87tuw74559.fsf@linux.ibm.com> (raw)
In-Reply-To: <20200818150736.GQ17456@casper.infradead.org>
Matthew Wilcox <willy@infradead•org> 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.
>
> #ifdef CONFIG_HUGETLB_PAGE
> if (PageCompound(page)) {
> flush_dcache_icache_hugepage(page);
> return;
> }
> #endif
I do have a change posted sometime back to avoid that confusion.
http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20200320103256.229365-1-aneesh.kumar@linux.ibm.com/
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.
prev parent reply other threads:[~2020-09-09 10:32 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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