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List:       linux-newbie
Subject:    mapping memory reserved by "memmap" kernel boot param into user space
From:       Jayram Déshpandé <jaydesh9 () gmail ! com>
Date:       2013-04-01 5:11:56
Message-ID: CAGj4Cuci1+tk55bSAVONT1O+Z+7kBce9CJ=7gspGXseGhsyaeQ () mail ! gmail ! com
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Hello ,

As discussed in this[1] discussion, i am reserving a memory chunk at the
boot time using a kernel boot parameter memmap=8G$64G

I have written a character driver [2] kernel module which , during
initialization does a ioremap of this reserved memory chunk. As explained
here , in my driver mmap all i need to do is remap_pfn_range for this
memory chunk pointer returned by the ioremap.

I am running this on 3.x linux kernel. My user space application opens this
memory chunk as a device mounted by the driver. When i do mmap from the use
space application i see a system hang. my dmesg don't provide me much
information.

So questions are :

1 ) Does  remap_pfn_range function have some upper limit on the size of the
memory that can be remaped to ? Note that i am trying to reserve a
comparatively large chunks of memory at the boot time of the order of 64GB
to about 150GB. The system can have 128 to 256 GB of ram.

2) I tried by disabling the ioremap from the initialization and thus
directly doing the page frame numbers remapping in the mmap ioctl routing.
But that also results in a hang.


3) I tried with a page-fault handler , but that doesn't seem to help either.




Regards,
-Jay


P.S. code can be found here [4]


[1] http:// stackoverflow.com/q/1911473/143897
[2] http:// pete.akeo.ie/2011/08/writing-linux-device-driver-for-kernels.html
[3] http:// www.
linuxquestions.org/questions/linux-kernel-70/mmap-of-several-gb-of-reserved-memory-using-805818/#post3972954
 [4] http:// stackoverflow.com/questions/12790382/mapping-memory-reserved-by-mmap-kernel-boot-param-into-user-space
                
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