From: Vivek Goyal <vgoyal@xxxxxxxxxx> Subject: Re: [RFC PATCH 0/5] crash dump bitmap: scan memory pages in kernel to speedup kernel dump process Date: Thu, 7 Mar 2013 10:21:08 -0500 > On Thu, Mar 07, 2013 at 10:58:18PM +0800, Jingbai Ma wrote: <cut> >> >> 2. Scans all memory pages in makedumpfile is a very slow process. On >> system with 1TB or more memory installed, the scanning process is very >> long. Typically on 1TB idle system, it takes about 19 minutes. On system >> with 4TB or more memory installed, it even doesn't work. To address the >> out of memory issue on system with big memory (4TB or more memory >> installed), makedumpfile v1.5.1 introduces a new cyclic mode. It only >> scans a piece of memory pages each time, and do it cyclically to scan >> all memory pages. But it runs more slowly, on 1TB system, takes about 33 >> minutes. > > One of the reasons it is slow because we don't support mmpa() interface. > That means for every read, we map 4K page, flush TLB, read it, unmap it > and flush TLB again. This is lot of processing overhead per 4K page. > > Hatayama is now working on making mmap() interface and allow user space > to bigger chunks of memory in one so. So that in one mmap() call we can > map a bigger range instead of just 4K. And his numbers show that it > has helped a lot. Yes, so when are you able to get down to reviewing the patch set? Thanks. HATAYAMA, Daisuke
