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ADoNJaizsC990KSUm65zAYUqgkXGWh+zAC81DDkwRY/DDBZASi8kuHmBnxdI36+z52j/5sSnEn+XKBaT8Kjop17Hk0EhWWG87XHpa4BRUMQphMYO/fkQjCgSmAx3j1knuTllweehioCfQXOt4wXs66ZFEL2kslWC+l/hV33agbJgUNFXp/y0Jq1NNUiHeQiMPedPbxDU0GPcziEYPXnmTY1l6cJrsDdoyl0+XxCjWGV64xoIqiHLoLfpY2v7MlN47sabkaOaCEVTCtghwa386tvivBDQL1ymtabOp1msLgae7MLC6hSJsFa8Mrhym5DSCRWF2OkvanNTXKZrkMfGyEENe4w== 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 1/31/2024 6:30 PM, David Hildenbrand wrote: > On 31.01.24 03:30, Yin Fengwei wrote: >> >> >> On 1/29/24 22:32, David Hildenbrand wrote: >>> +static inline pte_t get_and_clear_full_ptes(struct mm_struct *mm, >>> +        unsigned long addr, pte_t *ptep, unsigned int nr, int full) >>> +{ >>> +    pte_t pte, tmp_pte; >>> + >>> +    pte = ptep_get_and_clear_full(mm, addr, ptep, full); >>> +    while (--nr) { >>> +        ptep++; >>> +        addr += PAGE_SIZE; >>> +        tmp_pte = ptep_get_and_clear_full(mm, addr, ptep, full); >>> +        if (pte_dirty(tmp_pte)) >>> +            pte = pte_mkdirty(pte); >>> +        if (pte_young(tmp_pte)) >>> +            pte = pte_mkyoung(pte); >> I am wondering whether it's worthy to move the pte_mkdirty() and >> pte_mkyoung() >> out of the loop and just do it one time if needed. The worst case is >> that they >> are called nr - 1 time. Or it's just too micro? > > I also thought about just indicating "any_accessed" or "any_dirty" using > flags to the caller, to avoid the PTE modifications completely. Felt a > bit micro-optimized. > > Regarding your proposal: I thought about that as well, but my assumption > was that dirty+young are "cheap" to be set. > > On x86, pte_mkyoung() is setting _PAGE_ACCESSED. > pte_mkdirty() is setting _PAGE_DIRTY | _PAGE_SOFT_DIRTY, but it also has > to handle the saveddirty handling, using some bit trickery. > > So at least for pte_mkyoung() there would be no real benefit as far as I > can see (might be even worse). For pte_mkdirty() there might be a small > benefit. > > Is it going to be measurable? Likely not. Yeah. We can do more investigation when performance profiling call this out. Regards Yin, Fengwei > > Am I missing something? > > Thanks! >