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Message-ID: <alpine.LFD.1.10.0807010933180.20870@hp.linux-foundation.org> Date: Tue, 1 Jul 2008 09:35:34 -0700 (PDT) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Paul Mundt <lethal@...ux-sh.org> cc: Hideo Saito <saito@...san.co.jp>, linux-sh@...r.kernel.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: follow_page() performance regressions On Tue, 1 Jul 2008, Linus Torvalds wrote: > > - some cache issue on SH. ZERO_PAGE is a single page at a fixed virtual > address, while it used to populate the page tables with individual > pages. Normally, this should be *better* for caching, but maybe there > is some conflict? What kind of caches does SH have (virtually indexed?) Actually, this one is unlikely. ZERO_PAGE _used_ to be problematic on some virtually indexed caches, because the same physical page would get mapped into multiple places virtually, which in turn then caused some cache or TLB conflict or something (I forget - MIPS was the main offender). But because we now use just the single kernel virtual address for accessing the ZERO_PAGE, that really shouldn't matter. Unless the particular user of follow_pages() that triggers in this case is doing something odd, of course. Linus -- 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/
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