Re: [dm-devel] [PATCH] md/dm-ioctl.c: optimize memory allocation in copy_params

From: Zhang, Yanmin
Date: Thu Jul 24 2014 - 01:54:09 EST

On 2014/7/24 1:14, Mikulas Patocka wrote:

On Wed, 23 Jul 2014, Alasdair G Kergon wrote:

On Wed, Jul 23, 2014 at 08:16:58AM -0400, Mikulas Patocka wrote:
So, it means that you do not use device mapper at all. So, why are you
trying to change memory allocation in device mapper?
So the *test* they run is asking device-mapper to briefly reserve a 64KB
buffer when there is no data to report: The answer is not to run that
pointless test:)

And if a single 64KB allocation really is a big deal, then patch 'vold'
in userspace so it doesn't ask for 64KB when it clearly doesn't need it!

+ int Devmapper::dumpState(SocketClient *c) {
+ char *buffer = (char *) malloc(1024 * 64);

The code has just
for all the other dm ioctls it issues.

Only use a larger value when it is needed i.e. if DM_BUFFER_FULL_FLAG gets set.

Device mapper shouldn't depend on allocation on any contiguous memory - it
will fall back to vmalloc. I still can't believe that their suggested
patch makes any difference.

This pattern is being repeated over and over in the kernel - for example:

return vmalloc(count * sizeof(pid_t));
return kmalloc(count * sizeof(pid_t), GFP_KERNEL);

if (is_vmalloc_addr(p))

- I think we should make two functions that do this operation (for example
kvalloc and kvfree) and convert device mapper and other users to these
functions. Then, other kernel subsystems can start to use them to fix
memory fragmentation issues.

Thank Mikulas and Alasdair. Before sending out the patch, we know the result. :)
It's hard to balance between performance and stability.

Anyway, we would try to change seq_read.


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