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Date: Fri, 8 May 2015 16:40:35 -0400 From: "John Stoffel" <john@...ffel.org> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: John Stoffel <john@...ffel.org>, Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Dan Williams <dan.j.williams@...el.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Boaz Harrosh <boaz@...xistor.com>, Jan Kara <jack@...e.cz>, Mike Snitzer <snitzer@...hat.com>, Neil Brown <neilb@...e.de>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Heiko Carstens <heiko.carstens@...ibm.com>, Chris Mason <clm@...com>, Paul Mackerras <paulus@...ba.org>, "H. Peter Anvin" <hpa@...or.com>, Christoph Hellwig <hch@....de>, Alasdair Kergon <agk@...hat.com>, "linux-nvdimm\@lists.01.org" <linux-nvdimm@...1.01.org>, Mel Gorman <mgorman@...e.de>, Matthew Wilcox <willy@...ux.intel.com>, Ross Zwisler <ross.zwisler@...ux.intel.com>, Martin Schwidefsky <schwidefsky@...ibm.com>, Jens Axboe <axboe@...nel.dk>, "Theodore Ts'o" <tytso@....edu>, "Martin K. Petersen" <martin.petersen@...cle.com>, Julia Lawall <Julia.Lawall@...6.fr>, Tejun Heo <tj@...nel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH v2 00/10] evacuate struct page from the block layer, introduce __pfn_t >>>>> "Linus" == Linus Torvalds <torvalds@...ux-foundation.org> writes: Linus> On Fri, May 8, 2015 at 7:40 AM, John Stoffel <john@...ffel.org> wrote: >> >> Now go and look at your /home or /data/ or /work areas, where the >> endusers are actually keeping their day to day work. Photos, mp3, >> design files, source code, object code littered around, etc. Linus> However, the big files in that list are almost immaterial from a Linus> caching standpoint. Linus> Caching source code is a big deal - just try not doing it and Linus> you'll figure it out. And the kernel C source files used to Linus> have a median size around 4k. Caching any files is a big deal, and if I'm doing batch edits of large jpegs, won't they get cached as well? Linus> The big files in your home directory? Let me make an educated Linus> guess. Very few to *none* of them are actually in your page Linus> cache right now. And you'd never even care if they ever made Linus> it into your page cache *at*all*. Much less whether you could Linus> ever cache them using large pages using some very fancy cache. Hmm... probably not honestly, since I'm not a home and not using the system actively right now. But I can see situations where being able to mix different page sizes efficiently might be a good thing. Linus> There are big files that care about caches, but they tend to be Linus> binaries, and for other reasons (things like randomization) you Linus> would never want to use largepages for those anyway. Or large design files, like my users at $WORK use, which can be 4Gb in size for a large design, which is ASIC chip layout work. So I'm a little bit in the minority there. And yes I do have other users will millions of itty bitty files as well. Linus> So from a page cache standpoint, I think the 4kB size still Linus> matters. A *lot*. largepages are a complete red herring, and Linus> will continue to be so pretty much forever (anonymous Linus> largepages perhaps less so). I think in the future, being able to efficiently mix page sizes will become useful, if only to lower the memory overhead of keeping track of large numbers of pages. John -- 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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