From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Subject: Re: [PATCH v3 00/21] kdump, vmcore: support mmap() on /proc/vmcore Date: Tue, 19 Mar 2013 12:30:05 -0700 > On Sat, 16 Mar 2013 13:00:47 +0900 HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com> 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? > I designed it to keep backward-compatibility at least for gdb and binutils but not less for makedumpfile since it should follow kernel changes; old makedumpfile cannot use newer kernels, and this is within the range of this review. Thanks. HATAYAMA, Daisuke
