linux-kernel - RE: [PATCH v4 4/5] cramfs: add mmap support

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Date:   Thu, 5 Oct 2017 17:15:28 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Chris Brandt <Chris.Brandt@...esas.com>
cc:     Christoph Hellwig <hch@...radead.org>,
        Richard Weinberger <richard.weinberger@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-embedded@...r.kernel.org" <linux-embedded@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4 4/5] cramfs: add mmap support

On Thu, 5 Oct 2017, Chris Brandt wrote:

> On Wednesday, October 04, 2017, Nicolas Pitre wrote:
> > Anyway, here's a replacement for patch 4/5 below:
> > 
> > ----- >8
> > Subject: cramfs: add mmap support
> > 
> > When cramfs_physmem is used then we have the opportunity to map files
> > directly from ROM, directly into user space, saving on RAM usage.
> > This gives us Execute-In-Place (XIP) support.
> 
> 
> Tested on my setup:
>  * Cortex A9 (with MMU)
>  * CONFIG_XIP_KERNEL=y
>  * booted with XIP CRAMFS as my rootfs 
>  * all apps and libraries marked as XIP in my cramfs image
> 
> 
> 
> So far, functionally it seems to work the same as [PATCH v4 4/5].
> 
> As Nicolas said, before you could easily see that all my apps and 
> libraries were XIP from Flash:
> 
> $ cat /proc/self/maps
> 00008000-000a1000 r-xp 1b005000 00:0c 18192      /bin/busybox
> 000a9000-000aa000 rw-p 00099000 00:0c 18192      /bin/busybox
> 000aa000-000ac000 rw-p 00000000 00:00 0          [heap]
> b6e69000-b6f42000 r-xp 1b0bc000 00:0c 766540     /lib/libc-2.18-2013.10.so
> b6f42000-b6f4a000 ---p 1b195000 00:0c 766540     /lib/libc-2.18-2013.10.so
> b6f4a000-b6f4c000 r--p 000d9000 00:0c 766540     /lib/libc-2.18-2013.10.so
> b6f4c000-b6f4d000 rw-p 000db000 00:0c 766540     /lib/libc-2.18-2013.10.so
> b6f4d000-b6f50000 rw-p 00000000 00:00 0
> b6f50000-b6f67000 r-xp 1b0a4000 00:0c 670372     /lib/ld-2.18-2013.10.so
> b6f6a000-b6f6b000 rw-p 00000000 00:00 0
> b6f6c000-b6f6e000 rw-p 00000000 00:00 0
> b6f6e000-b6f6f000 r--p 00016000 00:0c 670372     /lib/ld-2.18-2013.10.so
> b6f6f000-b6f70000 rw-p 00017000 00:0c 670372     /lib/ld-2.18-2013.10.so
> beac0000-beae1000 rw-p 00000000 00:00 0          [stack]
> bebc9000-bebca000 r-xp 00000000 00:00 0          [sigpage]
> ffff0000-ffff1000 r-xp 00000000 00:00 0          [vectors]
> 
> 
> 
> But now just busybox looks like it's XIP:
> 
> $ cat /proc/self/maps
> 00008000-000a1000 r-xp 1b005000 00:0c 18192      /bin/busybox
> 000a9000-000aa000 rw-p 00099000 00:0c 18192      /bin/busybox
> 000aa000-000ac000 rw-p 00000000 00:00 0          [heap]
> b6e4d000-b6f26000 r-xp 00000000 00:0c 766540     /lib/libc-2.18-2013.10.so
> b6f26000-b6f2e000 ---p 000d9000 00:0c 766540     /lib/libc-2.18-2013.10.so
> b6f2e000-b6f30000 r--p 000d9000 00:0c 766540     /lib/libc-2.18-2013.10.so
> b6f30000-b6f31000 rw-p 000db000 00:0c 766540     /lib/libc-2.18-2013.10.so
> b6f31000-b6f34000 rw-p 00000000 00:00 0
> b6f34000-b6f4b000 r-xp 00000000 00:0c 670372     /lib/ld-2.18-2013.10.so
> b6f4e000-b6f4f000 rw-p 00000000 00:00 0
> b6f50000-b6f52000 rw-p 00000000 00:00 0
> b6f52000-b6f53000 r--p 00016000 00:0c 670372     /lib/ld-2.18-2013.10.so
> b6f53000-b6f54000 rw-p 00017000 00:0c 670372     /lib/ld-2.18-2013.10.so
> bec93000-becb4000 rw-p 00000000 00:00 0          [stack]
> befad000-befae000 r-xp 00000000 00:00 0          [sigpage]
> ffff0000-ffff1000 r-xp 00000000 00:00 0          [vectors]

Do you have the same amount of free memory once booted in both cases?

> Regardless, from a functional standpoint:
> 
> Tested-by: Chris Brandt <chris.brandt@...esas.com>

Thanks.

> Just FYI, the previous [PATCH v4 4/5] also included this (which was the 
> only real difference between v3 and v4):
> 
> 
> diff --git a/fs/cramfs/Kconfig b/fs/cramfs/Kconfig
> index 5b4e0b7e13..306549be25 100644
> --- a/fs/cramfs/Kconfig
> +++ b/fs/cramfs/Kconfig
> @@ -30,7 +30,7 @@ config CRAMFS_BLOCKDEV
>  
>  config CRAMFS_PHYSMEM
>  	bool "Support CramFs image directly mapped in physical memory"
> -	depends on CRAMFS
> +	depends on CRAMFS = y

Yeah, that was necessary because split_vma() wasn't exported to modules. 
Now split_vma() is no longer used so the no-module restriction has also 
been removed.


Nicolas