Messages in this thread | | | Date | Fri, 23 Mar 2007 10:14:52 +0000 | From | Christoph Hellwig <> | Subject | Re: [patch] cache pipe buf page address for non-highmem arch |
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On Thu, Mar 22, 2007 at 05:51:11PM -0700, Ken Chen wrote: > It is really sad that we always call kmap and friends for every pipe > buffer page on 64-bit arch that doesn't use HIGHMEM, or on > configuration that doesn't turn on HIGHMEM. > > The effect of calling kmap* is visible in the execution profile when > pipe code is being stressed. It is especially true on amd's x86-64 > platform where kmap() has to traverse through numa node index > calculation in order to convert struct page * to kernel virtual > address. It is fairly pointless to perform that calculation repeatly > on system with no highmem (i.e., 64-bit arch like x86-64). This patch > caches kernel pipe buffer page's kernel vaddr to speed up pipe buffer > mapping functions. > > There is another suboptimal block in pipe_read() where wake_up is > called twice. I think it was an oversight since in pipe_write(), it > looks like it is doing the right thing.
I think you're fixing the symptom here and not the cause. If calculating the virtual address of a page is so expensive on your setup it should define WANT_PAGE_VIRTUAL and we should always cache the virtual address in struct page. There's a lot more code, epecially in filesystems that's rather upset about a slow page_address.
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