linux-kernel - Re: [PATCH v3 14/14] libnvdimm, pmem: disable dax flushing when pmem is fronting a volatile region

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Message-ID: <CAPcyv4jyM5HqNw0efE+03ZzSN-4YnqSQ9z2jkx7nDBgqwSsg3w@mail.gmail.com>
Date:   Fri, 9 Jun 2017 16:21:16 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Cc:     Jan Kara <jack@...e.cz>, dm-devel@...hat.com,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jeff Moyer <jmoyer@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3 14/14] libnvdimm, pmem: disable dax flushing when pmem
 is fronting a volatile region

On Fri, Jun 9, 2017 at 1:25 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> The pmem driver attaches to both persistent and volatile memory ranges
> advertised by the ACPI NFIT. When the region is volatile it is redundant
> to spend cycles flushing caches at fsync(). Check if the hosting region
> is volatile and do not set QUEUE_FLAG_WC if it is.
>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Jeff Moyer <jmoyer@...hat.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Matthew Wilcox <mawilcox@...rosoft.com>
> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  drivers/nvdimm/pmem.c        |   13 ++++++++-----
>  drivers/nvdimm/region_devs.c |    6 ++++++
>  include/linux/libnvdimm.h    |    1 +
>  3 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index 06f6c27ec1e9..5cac9fb39db8 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -279,10 +279,10 @@ static int pmem_attach_disk(struct device *dev,
>         struct nd_namespace_io *nsio = to_nd_namespace_io(&ndns->dev);
>         struct nd_region *nd_region = to_nd_region(dev->parent);
>         struct vmem_altmap __altmap, *altmap = NULL;
> +       int nid = dev_to_node(dev), fua, wbc;
>         struct resource *res = &nsio->res;
>         struct nd_pfn *nd_pfn = NULL;
>         struct dax_device *dax_dev;
> -       int nid = dev_to_node(dev);
>         struct nd_pfn_sb *pfn_sb;
>         struct pmem_device *pmem;
>         struct resource pfn_res;
> @@ -308,9 +308,12 @@ static int pmem_attach_disk(struct device *dev,
>         dev_set_drvdata(dev, pmem);
>         pmem->phys_addr = res->start;
>         pmem->size = resource_size(res);
> -       if (!IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE)
> -                       || nvdimm_has_flush(nd_region) < 0)
> -               dev_warn(dev, "unable to guarantee persistence of writes\n");
> +       fua = nvdimm_has_flush(nd_region);
> +       if (!IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) || fua < 0)
> +               dev_warn(dev, "unable to guarantee persistence of writes\n"); {

I sent this patch with local uncommitted changes. Will send a v2
shortly, and also update stg mail to abort if the tree is dirty.