Messages in this thread | | | Date | Wed, 9 Sep 2009 10:44:23 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 7/8] mm: reinstate ZERO_PAGE |
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On Tue, 8 Sep 2009 12:56:57 +0100 (BST) Hugh Dickins <hugh.dickins@tiscali.co.uk> wrote:
> On Tue, 8 Sep 2009, KAMEZAWA Hiroyuki wrote: > > > > A nitpick but this was a concern you shown, IIUC. > > > > == __get_user_pages().. > > > > if (pages) { > > pages[i] = page; > > > > flush_anon_page(vma, page, start); > > flush_dcache_page(page); > > } > > == > > > > This part will call flush_dcache_page() even when ZERO_PAGE is found. > > > > Don't we need to mask this ? > > No, it's okay to flush_dcache_page() on ZERO_PAGE: we always used to > do that there, and the arches I remember offhand won't do anything > with it anyway, once they see page->mapping NULL. > > What you're remembering, that I did object to, was the way your > FOLL_NOZERO ended up doing > pages[i] = NULL; > flush_anon_page(vma, NULL, start); > flush_dcache_page(NULL); > > which would cause an oops when those arches look at page->mapping. > > I should take another look at your FOLL_NOZERO: I may have dismissed > it too quickly, after seeing that bug, and oopsing on x86 when > mlocking a readonly anonymous area. > > Though I like that we don't _need_ to change mlock.c for reinstated > ZERO_PAGE, this morning I'm having trouble persuading myself that > mlocking a readonly anonymous area is too silly to optimize for. > > Maybe the very people who persuaded you to bring back the anonymous > use of ZERO_PAGE, are also doing a huge mlock of the area first? No, as far as I know, they'll not do huge mlock.
Thanks, -Kame
> So if two or more are starting up at the same time on the same box, > more bouncing than is healthy (and more than they would have seen > in the old days of ZERO_PAGE but no lock_page on it there). > > I'd like to persuade myself not to bother, > but may want to add a further patch for that later. > > Hugh > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> >
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