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Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: anton@mips.complang.tuwien.ac.at (Anton Ertl) Newsgroups: comp.arch Subject: transparent huge pages (was: Address bits again) Date: Thu, 05 Sep 2024 13:45:13 GMT Organization: Institut fuer Computersprachen, Technische Universitaet Wien Lines: 20 Message-ID: <2024Sep5.154513@mips.complang.tuwien.ac.at> References: <vb9r4g$2o1f$1@gal.iecc.com> <memo.20240904163805.19028V@jgd.cix.co.uk> <Cu0CO.120079$8jx2.14596@fx17.iad> Injection-Date: Thu, 05 Sep 2024 15:55:36 +0200 (CEST) Injection-Info: dont-email.me; posting-host="f078a70d8fd09bf20845f2d2f555f93d"; logging-data="382148"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19KNMnLl9iRrud9yAmJmhbA" Cancel-Lock: sha1:PNzakBAXMhbA/mFs32pOSOM6vlY= X-newsreader: xrn 10.11 Bytes: 1919 scott@slp53.sl.home (Scott Lurndal) writes: >Linux supports THP (Transparent Huge Pages) were the OS automatically >updates the translation table to coalsce smaller pages into larger blocks >on intel/amd/arm64 processors. I have seen good effects from THP a number of years ago: I has seen a matrix multiply program miss the TLB every time on one of its input matrices. And then I ran it again, and the effect was gone. Eventually I found out that this is due to THP, and I have to disable THP if I want to demonstrate that effect to my students. Recently, I thought that by using a 2MB size for an mmap()-allocated memory block I would get THP on Linux. Unfortunately, mmap() does not aligng 2MB blocks to 2MB boundaries, and if it does not, the block is not eligible for THP. This was disappointing. - anton -- 'Anyone trying for "industrial quality" ISA should avoid undefined behavior.' Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>