From: Catalin Marinas <catalin.marinas@arm.com>
To: "liwei (CM)" <liwei213@huawei.com>
Cc: "Song Bao Hua \(Barry Song\)" <song.bao.hua@hisilicon.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"steve.capper@arm.com" <steve.capper@arm.com>,
"Chenfeng \(puck\)" <puck.chen@hisilicon.com>,
sujunfei <sujunfei2@hisilicon.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
fengbaopeng <fengbaopeng2@hisilicon.com>,
zhaojiapeng <zhaojiapeng@huawei.com>,
"Xiaqing \(A\)" <saberlily.xia@hisilicon.com>,
Mike Rapoport <rppt@linux.ibm.com>,
"will@kernel.org" <will@kernel.org>,
"nsaenzjulienne@suse.de" <nsaenzjulienne@suse.de>,
butao <butao@hisilicon.com>
Subject: Re: 答复: 答复: [PATCH] arm64: mm: free unused memmap for sparse memory model that define VMEMMAP
Date: Thu, 23 Jul 2020 12:29:26 +0100 [thread overview]
Message-ID: <20200723112926.GB7315@gaia> (raw)
In-Reply-To: <1699CE87DE933F49876AD744B5DC140F2312F0D6@dggemm526-mbx.china.huawei.com>
On Wed, Jul 22, 2020 at 01:40:34PM +0000, liwei (CM) wrote:
> Catalin Marinas wrote:
> > On Wed, Jul 22, 2020 at 08:41:17AM +0000, liwei (CM) wrote:
> > > Mike Rapoport wrote:
> > > > On Tue, Jul 21, 2020 at 03:32:03PM +0800, Wei Li wrote:
> > > > > For the memory hole, sparse memory model that define
> > > > > SPARSEMEM_VMEMMAP do not free the reserved memory for the page
> > > > > map, this patch do it.
> > > >
> > > > Are there numbers showing how much memory is actually freed?
> > > >
> > > > The freeing of empty memmap would become rather complex with these
> > > > changes, do the memory savings justify it?
> > >
> > > In the sparse memory model, the size of a section is 1 GB
> > > (SECTION_SIZE_BITS 30) by default.
> >
> > Can we reduce SECTION_SIZE_BITS instead? Say 26?
>
> Yes, you are right, reduce SECTION_SIZE_BITS to 26 can save almost the
> same memory as the patch.
>
> 1) However, it is not clear whether changing the section size has any
> other impact.
Well, we should analyse this.
> 2) Just like the flat memory model and the sparse memory model that
> does not define VMEMMAP, both of them have their own ways to free
> unused memmap. I think we've given a similar way for sparse memory
> define VMEMMAP.
I think we did it for flatmem initially (on arm32) and added support for
sparsemem later on, so free_unused_memmap() had to cope with sparse
sections. On arm64 we introduced vmemmap support and didn't bother with
the freeing at all because of the added complexity of the vmemmap page
tables.
I wonder whether we should just disallow flatmem and non-vmemmap
sparsemem on arm64. Is there any value in keeping them around?
> 3) This explicit free unused memmap method does reduce unnecessary
> memory waste for users who do not notice the section size
> modification.
But if we changed SECTION_SIZE_BITS in the mainline kernel, then we
wouldn't need additional code to free the unused memmap.
--
Catalin
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next prev parent reply other threads:[~2020-07-23 11:31 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 7:32 [PATCH] arm64: mm: free unused memmap for sparse memory model that define VMEMMAP Wei Li
2020-07-22 6:07 ` Mike Rapoport
2020-07-22 8:41 ` 答复: " liwei (CM)
2020-07-22 12:49 ` Catalin Marinas
2020-07-22 13:40 ` 答复: " liwei (CM)
2020-07-23 11:29 ` Catalin Marinas [this message]
2020-07-23 13:18 ` Mike Rapoport
2020-07-24 3:40 ` 答复: " liwei (CM)
2020-07-23 2:33 ` Anshuman Khandual
2020-07-23 3:28 ` 答复: " liwei (CM)
[not found] <20200708015555.14946-1-liwei213@huawei.com>
2020-07-08 7:18 ` Song Bao Hua (Barry Song)
2020-07-08 7:51 ` 答复: " liwei (CM)
2020-07-09 12:27 ` Song Bao Hua (Barry Song)
2020-07-21 1:56 ` 答复: " liwei (CM)
2020-07-21 6:35 ` Mike Rapoport
2020-07-21 12:27 ` 答复: " liwei (CM)
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