linux-kernel - Re: [patch] cache pipe buf page address for non-highmem arch

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20070323101452.GA15144@infradead.org>
Date:	Fri, 23 Mar 2007 10:14:52 +0000
From:	Christoph Hellwig <hch@...radead.org>
To:	Ken Chen <kenchen@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] cache pipe buf page address for non-highmem arch

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.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/