linux-kernel - [PATCH] libnvdimm, namespace: make min namespace size 4K

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Date:   Fri, 02 Feb 2018 00:30:32 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     linux-nvdimm@...ts.01.org
Cc:     ross.zwisler@...ux.intel.com, linux-kernel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>,
        Cheng-mean Liu <soccerl@...rosoft.com>
Subject: [PATCH] libnvdimm, namespace: make min namespace size 4K

The arbitrary 4MB minimum namespace size turns out to be too large for
some environments. Quoting Cheng-mean Liu:

    In the case of emulated NVDIMM devices in the VM environment, there
    are scenarios that NVDIMM device with much smaller sizes are
    desired, for example, we might use a single enumerated NVDIMM DAX
    device for representing each container layer, which in some cases
    could be just a few KBs size.

PAGE_SIZE is the minimum where we can still support DAX of at least
a single page.

Cc: Matthew Wilcox <willy@...radead.org>
Reported-by: Cheng-mean Liu <soccerl@...rosoft.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 include/uapi/linux/ndctl.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/ndctl.h b/include/uapi/linux/ndctl.h
index 30ef1236aafa..7e27070b9440 100644
--- a/include/uapi/linux/ndctl.h
+++ b/include/uapi/linux/ndctl.h
@@ -209,7 +209,7 @@ enum nd_driver_flags {
 };
 
 enum {
-	ND_MIN_NAMESPACE_SIZE = 0x00400000,
+	ND_MIN_NAMESPACE_SIZE = PAGE_SIZE,
 };
 
 enum ars_masks {