From: Dan Williams <dan.j.williams@intel.com>
To: Toshi Kani <toshi.kani@hp.com>
Cc: Borislav Petkov <bp@alien8.de>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Arnd Bergmann <arnd@arndb.de>,
linux-mm@kvack.org,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
X86 ML <x86@kernel.org>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
jgross@suse.com, Stefan Bader <stefan.bader@canonical.com>,
Andy Lutomirski <luto@amacapital.net>,
hmh@hmh.eng.br, yigal@plexistor.com,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
"Elliott, Robert (Server Storage)" <Elliott@hp.com>,
mcgrof@suse.com, Christoph Hellwig <hch@lst.de>,
Matthew Wilcox <willy@linux.intel.com>
Subject: Re: [PATCH v10 12/12] drivers/block/pmem: Map NVDIMM with ioremap_wt()
Date: Fri, 29 May 2015 11:19:57 -0700 [thread overview]
Message-ID: <CAPcyv4g+zYFkEYpa0HCh0Q+2C3wWNr6v3ZU143h52OKf=U=Qvw@mail.gmail.com> (raw)
In-Reply-To: <1432911782.23540.55.camel@misato.fc.hp.com>
On Fri, May 29, 2015 at 8:03 AM, Toshi Kani <toshi.kani@hp.com> wrote:
> On Fri, 2015-05-29 at 07:43 -0700, Dan Williams wrote:
>> On Fri, May 29, 2015 at 2:11 AM, Borislav Petkov <bp@alien8.de> wrote:
>> > On Wed, May 27, 2015 at 09:19:04AM -0600, Toshi Kani wrote:
>> >> The pmem driver maps NVDIMM with ioremap_nocache() as we cannot
>> >> write back the contents of the CPU caches in case of a crash.
>> >>
>> >> This patch changes to use ioremap_wt(), which provides uncached
>> >> writes but cached reads, for improving read performance.
>> >>
>> >> Signed-off-by: Toshi Kani <toshi.kani@hp.com>
>> >> ---
>> >> drivers/block/pmem.c | 4 ++--
>> >> 1 file changed, 2 insertions(+), 2 deletions(-)
>> >>
>> >> diff --git a/drivers/block/pmem.c b/drivers/block/pmem.c
>> >> index eabf4a8..095dfaa 100644
>> >> --- a/drivers/block/pmem.c
>> >> +++ b/drivers/block/pmem.c
>> >> @@ -139,11 +139,11 @@ static struct pmem_device *pmem_alloc(struct device *dev, struct resource *res)
>> >> }
>> >>
>> >> /*
>> >> - * Map the memory as non-cachable, as we can't write back the contents
>> >> + * Map the memory as write-through, as we can't write back the contents
>> >> * of the CPU caches in case of a crash.
>> >> */
>> >> err = -ENOMEM;
>> >> - pmem->virt_addr = ioremap_nocache(pmem->phys_addr, pmem->size);
>> >> + pmem->virt_addr = ioremap_wt(pmem->phys_addr, pmem->size);
>> >> if (!pmem->virt_addr)
>> >> goto out_release_region;
>> >
>> > Dan, Ross, what about this one?
>> >
>> > ACK to pick it up as a temporary solution?
>>
>> I see that is_new_memtype_allowed() is updated to disallow some
>> combinations, but the manual seems to imply any mixing of memory types
>> is unsupported. Which worries me even in the current code where we
>> have uncached mappings in the driver, and potentially cached DAX
>> mappings handed out to userspace.
>
> is_new_memtype_allowed() is not to allow some combinations of mixing of
> memory types. When it is allowed, the requested type of ioremap_xxx()
> is changed to match with the existing map type, so that mixing of memory
> types does not happen.
Yes, but now if the caller was expecting one memory type and gets
another one that is something I think the driver would want to know.
At a minimum I don't think we want to get emails about pmem driver
performance problems when someone's platform is silently degrading WB
to UC for example.
> DAX uses vm_insert_mixed(), which does not even check the existing map
> type to the physical address.
Right, I think that's a problem...
>> A general quibble separate from this patch is that we don't have a way
>> of knowing if ioremap() will reject or change our requested memory
>> type. Shouldn't the driver be explicitly requesting a known valid
>> type in advance?
>
> I agree we need a solution here.
>
>> Lastly we now have the PMEM API patches from Ross out for review where
>> he is assuming cached mappings with non-temporal writes:
>> https://lists.01.org/pipermail/linux-nvdimm/2015-May/000929.html.
>> This gives us WC semantics on writes which I believe has the nice
>> property of reducing the number of write transactions to memory.
>> Also, the numbers in the paper seem to be assuming DAX operation, but
>> this ioremap_wt() is in the driver and typically behind a file system.
>> Are the numbers relevant to that usage mode?
>
> I have not looked into the Ross's changes yet, but they do not seem to
> replace the use of ioremap_nocache(). If his changes can use WB type
> reliably, yes, we do not need a temporary solution of using ioremap_wt()
> in this driver.
Hmm, yes you're right, it seems those patches did not change the
implementation to use ioremap_cache()... which happens to not be
implemented on all architectures. I'll take a look.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2015-05-29 18:20 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-27 15:18 [PATCH v10 0/12] Support Write-Through mapping on x86 Toshi Kani
2015-05-27 15:18 ` [PATCH v10 1/12] x86, mm, pat: Set WT to PA7 slot of PAT MSR Toshi Kani
2015-05-27 15:18 ` [PATCH v10 2/12] x86, mm, pat: Change reserve_memtype() for WT Toshi Kani
2015-05-27 15:18 ` [PATCH v10 3/12] x86, asm: Change is_new_memtype_allowed() " Toshi Kani
2015-05-27 15:18 ` [PATCH v10 4/12] x86, mm, asm-gen: Add ioremap_wt() " Toshi Kani
2015-05-27 15:18 ` [PATCH v10 5/12] arch/*/asm/io.h: Add ioremap_wt() to all architectures Toshi Kani
2015-05-27 15:18 ` [PATCH v10 6/12] video/fbdev, asm/io.h: Remove ioremap_writethrough() Toshi Kani
2015-05-27 15:18 ` [PATCH v10 7/12] x86, mm, pat: Add pgprot_writethrough() for WT Toshi Kani
2015-05-27 15:19 ` [PATCH v10 8/12] x86, mm, asm: Add WT support to set_page_memtype() Toshi Kani
2015-05-27 15:19 ` [PATCH v10 9/12] x86, mm: Add set_memory_wt() for WT Toshi Kani
2015-05-27 15:19 ` [PATCH v10 10/12] x86, mm, pat: Cleanup init flags in pat_init() Toshi Kani
2015-05-29 8:59 ` Borislav Petkov
2015-05-27 15:19 ` [PATCH v10 11/12] x86, mm, pat: Refactor !pat_enabled handling Toshi Kani
2015-05-29 8:58 ` Borislav Petkov
2015-05-29 14:27 ` Toshi Kani
2015-05-29 15:13 ` Borislav Petkov
2015-05-29 15:17 ` Toshi Kani
2015-05-27 15:19 ` [PATCH v10 12/12] drivers/block/pmem: Map NVDIMM with ioremap_wt() Toshi Kani
2015-05-29 9:11 ` Borislav Petkov
2015-05-29 14:43 ` Dan Williams
2015-05-29 15:03 ` Toshi Kani
2015-05-29 18:19 ` Dan Williams [this message]
2015-05-29 18:32 ` Toshi Kani
2015-05-29 19:34 ` Dan Williams
2015-05-29 20:10 ` Toshi Kani
2015-05-29 18:34 ` Andy Lutomirski
2015-05-29 19:32 ` Dan Williams
2015-05-29 21:29 ` Elliott, Robert (Server Storage)
2015-05-29 21:46 ` Andy Lutomirski
2015-05-29 22:24 ` Elliott, Robert (Server Storage)
2015-05-29 22:32 ` H. Peter Anvin
2015-06-01 8:58 ` Ingo Molnar
2015-06-01 17:10 ` Andy Lutomirski
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAPcyv4g+zYFkEYpa0HCh0Q+2C3wWNr6v3ZU143h52OKf=U=Qvw@mail.gmail.com' \
--to=dan.j.williams@intel.com \
--cc=Elliott@hp.com \
--cc=akpm@linux-foundation.org \
--cc=arnd@arndb.de \
--cc=bp@alien8.de \
--cc=hch@lst.de \
--cc=hmh@hmh.eng.br \
--cc=hpa@zytor.com \
--cc=jgross@suse.com \
--cc=konrad.wilk@oracle.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-nvdimm@lists.01.org \
--cc=luto@amacapital.net \
--cc=mcgrof@suse.com \
--cc=mingo@redhat.com \
--cc=ross.zwisler@linux.intel.com \
--cc=stefan.bader@canonical.com \
--cc=tglx@linutronix.de \
--cc=toshi.kani@hp.com \
--cc=willy@linux.intel.com \
--cc=x86@kernel.org \
--cc=yigal@plexistor.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).