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U2FsdGVkX19jrHeI+dCGIibm8LEKarg4AuKBF0tMROhw9vHCh9FIbZ4dS8Xy7V1Z/QQI+8p5cbizw4WuABSbC4yWtuxtiDy3+XHp8zFATA3tSkbPjB95XzGbRz4i7fegN0+iotypmx76SbiCBf29njDEdTaSol5na9YK5Fkxky5l14Sq9mzuLjTHrDz+6oo4R/lae/R0jNtU1jtXWHxXWBr3qP8mjxpjTvvvDGNkLEVuvITAdbtSH5Sw3pSSHd+d+YREClSqMd/qHAVXeISnQSYGp/6N34fBdktUBXCNtDOLCc/USk6aJw3PaLvsed6rZ55Z5ZHDBHR46dnx2MAqhb68y8kCtnqMiDzRVAl7dvXAJ8SXWOWt1/oQp62n58fRfd+KNs2MiXe25INJn5ez00DIeDo+5VD7Dw6VxfqFuOPl6ZEVS/oE2Ye5wRdP8JkwuKlWMDoKpMaZCerwWIvA1D5gTELolihzCtQoa6CnAA6JjsuO4CLCt7R+7ZmSCBMezznavpNicQEhhI8g+JjNWlXbNeWlNF8aUWpJPsWGDSF8wYIAK4WnDtsReq1QvYefltRKwWA2qjAhzDaHyFU9PbwS96j2low9asPmEjlB8wCvUCes2oEshM5iRPXfHxsaM4T9UfCFY6pffQ0BJSzWUszuSbJFVmpzaaRq01xxPALWeXb9IKUXLwavqvYhSIPnhXXiVAdXLF8gcu3LiJw2PfLD5EDHNNFc8Zkwt2LFT3xAZg//uS8wQUbV4S4hfBQdQFwYasNpli3RaB71sFf/2ekWknOtT1nx/AFJ3vPof9uUqlQhy2H66V29V1kBfWfp1PT5J5KsnOxbSIwlrglYPsz4AtSE4t02fAjxBuJEq9ba9JF+O44befZf1ZtkiALbmen2kJRZvk8e4DqJhsGtugUNxDspDXtZT4n30T/qft3rQqs/U3TAFCCHDYvHrfI9oBirWn77js/NDIdQQY9 SbST4CMn 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/29/25 4:52 AM, Ryan Roberts wrote: > The common case for split_kernel_leaf_mapping() is for a single page. > Let's optimize this by only calling split_kernel_leaf_mapping_locked() > once. > > Since the start and end address are PAGE_SIZE apart, they must be > contained within the same contpte block. Further, if start is at the > beginning of the block or end is at the end of the block, then the other > address must be in the _middle_ of the block. So if we split on this > middle-of-the-contpte-block address, it is guaranteed that the > containing contpte block is split to ptes and both start and end are > therefore mapped by pte. > > This avoids the second call to split_kernel_leaf_mapping_locked() > meaning we only have to walk the pgtable once. > > Signed-off-by: Ryan Roberts > --- > arch/arm64/mm/mmu.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 114b88216b0c..8b5b19e1154b 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -740,9 +740,21 @@ int split_kernel_leaf_mapping(unsigned long start, unsigned long end) > mutex_lock(&pgtable_split_lock); > arch_enter_lazy_mmu_mode(); > > - ret = split_kernel_leaf_mapping_locked(start); > - if (!ret) > - ret = split_kernel_leaf_mapping_locked(end); > + /* > + * Optimize for the common case of splitting out a single page from a > + * larger mapping. Here we can just split on the "least aligned" of > + * start and end and this will guarantee that there must also be a split > + * on the more aligned address since the both addresses must be in the > + * same contpte block and it must have been split to ptes. > + */ > + if (end - start == PAGE_SIZE) { > + start = __ffs(start) < __ffs(end) ? start : end; > + ret = split_kernel_leaf_mapping_locked(start); This makes sense to me. I suggested the same thing in the discussion with Dev for v5. I'd like to have this patch squashed into patch #3. Thanks, Yang > + } else { > + ret = split_kernel_leaf_mapping_locked(start); > + if (!ret) > + ret = split_kernel_leaf_mapping_locked(end); > + } > > arch_leave_lazy_mmu_mode(); > mutex_unlock(&pgtable_split_lock);