Re: [PATCH v3 00/21] kdump, vmcore: support mmap() on /proc/vmcore
From: Andrew Morton
Date: Tue Mar 19 2013 - 15:30:18 EST
On Sat, 16 Mar 2013 13:00:47 +0900 HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx> wrote:
> Currently, read to /proc/vmcore is done by read_oldmem() that uses
> ioremap/iounmap per a single page. For example, if memory is 1GB,
> ioremap/iounmap is called (1GB / 4KB)-times, that is, 262144
> times. This causes big performance degradation.
> In particular, the current main user of this mmap() is makedumpfile,
> which not only reads memory from /proc/vmcore but also does other
> processing like filtering, compression and IO work. Update of page
> table and the following TLB flush makes such processing much slow;
> though I have yet to make patch for makedumpfile and yet to confirm
> how it's improved.
> To address the issue, this patch implements mmap() on /proc/vmcore to
> improve read performance. My simple benchmark shows the improvement
> from 200 [MiB/sec] to over 50.0 [GiB/sec].
There are quite a lot of userspace-visible vmcore changes here. Is it
all fully back-compatible? Will all known userspace continue to work
OK on newer kernels?
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/