From 1c4b406ee89c2c4210f2e19b97d39215f445c316 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 17 Sep 2018 16:29:15 +0200 Subject: [PATCH] x86/mm/cpa: Optimize same protection check When the existing mapping is correct and the new requested page protections are the same as the existing ones, then further checks can be omitted and the large page can be preserved. The slow path 4k wise check will not come up with a different result. Before: 1G pages checked: 2 1G pages sameprot: 0 1G pages preserved: 0 2M pages checked: 540 2M pages sameprot: 466 2M pages preserved: 47 4K pages checked: 800709 4K pages set-checked: 7668 After: 1G pages checked: 2 1G pages sameprot: 0 1G pages preserved: 0 2M pages checked: 538 2M pages sameprot: 466 2M pages preserved: 47 4K pages checked: 560642 4K pages set-checked: 7668 Signed-off-by: Thomas Gleixner Reviewed-by: Dave Hansen Cc: Peter Zijlstra Cc: Bin Yang Cc: Mark Gross Link: https://lkml.kernel.org/r/20180917143546.424477581@linutronix.de --- arch/x86/mm/pageattr.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 19781b0a..5160334 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -840,6 +840,20 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address, } /* + * Optimization: If the requested pgprot is the same as the current + * pgprot, then the large page can be preserved and no updates are + * required independent of alignment and length of the requested + * range. The above already established that the current pgprot is + * correct, which in consequence makes the requested pgprot correct + * as well if it is the same. The static protection scan below will + * not come to a different conclusion. + */ + if (pgprot_val(req_prot) == pgprot_val(old_prot)) { + cpa_inc_lp_sameprot(level); + return 0; + } + + /* * Make sure that the requested pgprot does not violate the static * protections. Check the full large page whether one of the pages * in it results in a different pgprot than the first one of the -- 2.7.4