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From: Christoph Hellwig <hch@infradead.org>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: linux-mm@kvack.org, linux-arch@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	x86@kernel.org, linuxppc-dev@lists.ozlabs.org,
	linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 4/4] mm/vmalloc: Hugepage vmalloc mappings
Date: Tue, 14 Apr 2020 00:23:16 -0700	[thread overview]
Message-ID: <20200414072316.GA5503@infradead.org> (raw)
In-Reply-To: <20200413125303.423864-5-npiggin@gmail.com>

On Mon, Apr 13, 2020 at 10:53:03PM +1000, Nicholas Piggin wrote:
> For platforms that define HAVE_ARCH_HUGE_VMAP and support PMD vmap mappings,
> have vmalloc attempt to allocate PMD-sized pages first, before falling back
> to small pages. Allocations which use something other than PAGE_KERNEL
> protections are not permitted to use huge pages yet, not all callers expect
> this (e.g., module allocations vs strict module rwx).
> 
> This gives a 6x reduction in dTLB misses for a `git diff` (of linux), from
> 45600 to 6500 and a 2.2% reduction in cycles on a 2-node POWER9.
> 
> This can result in more internal fragmentation and memory overhead for a
> given allocation. It can also cause greater NUMA unbalance on hashdist
> allocations.
> 
> There may be other callers that expect small pages under vmalloc but use
> PAGE_KERNEL, I'm not sure if it's feasible to catch them all. An
> alternative would be a new function or flag which enables large mappings,
> and use that in callers.

Why do we even use vmalloc in this case rather than just doing a huge
page allocation?  What callers are you intersted in?


  parent reply	other threads:[~2020-04-14  7:23 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-13 12:52 [PATCH v2 0/4] huge vmalloc mappings Nicholas Piggin
2020-04-13 12:53 ` [PATCH v2 1/4] mm/vmalloc: fix vmalloc_to_page for huge vmap mappings Nicholas Piggin
2020-04-13 13:34   ` Matthew Wilcox
2020-04-14 11:31     ` Nicholas Piggin
2020-04-13 12:53 ` [PATCH v2 2/4] mm: Move ioremap page table mapping function to mm/ Nicholas Piggin
2020-04-13 12:53 ` [PATCH v2 3/4] mm: HUGE_VMAP arch query functions cleanup Nicholas Piggin
2020-04-13 20:17   ` kbuild test robot
2020-04-13 20:29   ` kbuild test robot
2020-04-13 23:56   ` kbuild test robot
2020-04-13 23:56   ` [PATCH] mm: fix boolreturn.cocci warnings kbuild test robot
2020-04-13 12:53 ` [PATCH v2 4/4] mm/vmalloc: Hugepage vmalloc mappings Nicholas Piggin
2020-04-13 13:41   ` Matthew Wilcox
2020-04-14 11:39     ` Nicholas Piggin
2020-04-14 12:28     ` Christophe Leroy
2020-04-14 14:20       ` Matthew Wilcox
2020-04-14  7:23   ` Christoph Hellwig [this message]
2020-04-14 12:13     ` Nicholas Piggin
2020-04-14 13:02       ` Christoph Hellwig
2020-04-14 14:48         ` Nicholas Piggin
2020-04-15 10:47   ` Will Deacon
2020-04-16  2:38     ` Nicholas Piggin
2020-07-01  7:10   ` Zefan Li
2020-07-03  0:15     ` Nicholas Piggin
2020-07-20  2:02   ` Zefan Li
2020-07-20  2:49     ` Nicholas Piggin
2020-04-14  0:27 ` [PATCH v2 0/4] huge " David Rientjes
2020-04-14 12:23   ` Nicholas Piggin

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