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U2FsdGVkX1+KarCRHVijtz5j+Rt2NB+SYX5LEk/L3dNASYdyB0BgTDnMXi/izO45nWQci/NMShlvnWEczlKERqpht5jPl7fLMLwvuIgJdoDhv5KTSM9PtOoOSJqqUZsXo5BmLbXHEiYUcfBFtrUFS4Zq5qDrHXF8+p8BanumYZLX+BGRXlNn/ZRNTOemDmDPJbXLfWwAlR2dEnnd+aCe7TW8S27KtMZp2Bw4d/LwpOJg7hpUzellEsdkFp91aK97GqAD+zdK7a6dBz0XDMPckXxvgOJcIYIw2bF+pzmZiMqD/QWURQwZyyRniQJm9/ektRTj/70CA0OE/iXPR/+KRdyhKm1t8Gp1cgF64Ls2jOeR6n4byoqWFLBxyGY4rdgSXJJxNDeD3CwR1C6MXRut58JJS8DXMSUJ4dfhJfjNouhk0SYK5QjfXMFY7ErPuDOmVNlrdlpkUEW3bkNz3T5I9+jMReTWceBAkHD4bAMGq8Mq8Y5S4E5/wQYWWRtDGXnFloHsxGh7FdPiW0Q8/PfuRUoT2qZoCzwHs+fz8uS8AN1tazerN5Tdx121bEzEM9T9AP2CC8OILWn4g/alSTWRJoGoKnZK3wkiSflwxYGSkxJ/0GQzh8XakRe53S/hMVFdI59gnkU4jaV/T05s+f8eDpYSkjeiYg5yqJ2V3GV47/hrJ599ZHDRfJHH6IoM0JF95nHD0O82I3yJeOg7seG119neWiuFMr146jZ+ST9PTyq+m4PESv/AQ65tc2PTUjBVdkTrxEnXKimZ+E5uEdhVNBcsfgwh86OhdiZQxjJTjxtRkZtgXPu7GQWSiD5yqsHLzWQxoM2LFBaRAVg6VA4bLBbXY+ZP8iz/pCxEHveduFhrPVKPwpLt3Uwyx+WDpNSl27wfAu0S2D+s7EoxfJyKCuhNT1BROGRgoyGMcbIgxG+k05fGbZnSf1PHJeJRGRokPFjm1yHaowhKROiorfC cFprpPbc KsWEC7ZMeFCq6EUK6A0bCo+pQ1G2+JIxpXJrPVvGUEc/e2yi9K/fZ2fv+Y8lzGkRC7sCpI9GMedRn0qp7n0D8Ri9yMwHdnugl+uek0CN0Sl+sj6ZSXJeZkCRQA21Pxx+ETNPxaIrTBlEE5Su0bmsK2nws5rBl9alRsAAhT7WctnVYFX0J7q8Uf2QT583KqGx4nvdAtCfviWVp/uXYj5eLePZRcj+vu2ypmvIi4i7V3Fc53S7meT/x/ZlKPnrSfSVzBMcHEZsyJyjUblb8HXHY/OAc+Sn0DwNbeUJMNNuNZmbHB9ELngZJl0zODZAxDWRc7IfAGIWG0eKCYNBLhAzLEMHlXvp1wW3wp1JTpRgiQCNgFd1DYpz4rNs02CkpBhfCAPuqIv/IVp+UKPyL4aZoxj4ynPE7us68cbry 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: On 7/26/23 11:26, Yu Zhao wrote: > On Tue, Jul 25, 2023 at 8:49 PM Yin Fengwei wrote: >> >> >> On 7/25/23 13:55, Yu Zhao wrote: >>> On Fri, Jul 21, 2023 at 3:41 AM Yin Fengwei wrote: >>>> >>>> Currently, in function madvise_cold_or_pageout_pte_range(), the >>>> young bit of pte/pmd is cleared notify subscripter. >>>> >>>> Using notify-able API to make sure the subscripter is signaled about >>>> the young bit clearing. >>>> >>>> Signed-off-by: Yin Fengwei >>>> --- >>>> mm/madvise.c | 18 ++---------------- >>>> 1 file changed, 2 insertions(+), 16 deletions(-) >>>> >>>> diff --git a/mm/madvise.c b/mm/madvise.c >>>> index f12933ebcc24..b236e201a738 100644 >>>> --- a/mm/madvise.c >>>> +++ b/mm/madvise.c >>>> @@ -403,14 +403,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, >>>> return 0; >>>> } >>>> >>>> - if (pmd_young(orig_pmd)) { >>>> - pmdp_invalidate(vma, addr, pmd); >>>> - orig_pmd = pmd_mkold(orig_pmd); >>>> - >>>> - set_pmd_at(mm, addr, pmd, orig_pmd); >>>> - tlb_remove_pmd_tlb_entry(tlb, pmd, addr); >>>> - } >>>> - >>>> + pmdp_clear_flush_young_notify(vma, addr, pmd); >>>> folio_clear_referenced(folio); >>>> folio_test_clear_young(folio); >>>> if (folio_test_active(folio)) >>>> @@ -496,14 +489,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, >>>> >>>> VM_BUG_ON_FOLIO(folio_test_large(folio), folio); >>>> >>>> - if (pte_young(ptent)) { >>>> - ptent = ptep_get_and_clear_full(mm, addr, pte, >>>> - tlb->fullmm); >>>> - ptent = pte_mkold(ptent); >>>> - set_pte_at(mm, addr, pte, ptent); >>>> - tlb_remove_tlb_entry(tlb, pte, addr); >>>> - } >>>> - >>>> + ptep_clear_flush_young_notify(vma, addr, pte); >>> >>> These two places are tricky. >>> >>> I agree there is a problem here, i.e., we are not consulting the mmu >>> notifier. In fact, we do pageout on VMs on ChromeOS, and it's been a >>> known problem to me for a while (not a high priority one). >>> >>> tlb_remove_tlb_entry() is batched flush, ptep_clear_flush_young() is >>> not. But, on x86, we might see a performance improvement since >>> ptep_clear_flush_young() doesn't flush TLB at all. On ARM, there might >>> be regressions though. >>> >>> I'd go with ptep_clear_young_notify(), but IIRC, Minchan mentioned he >>> prefers flush. So I'll let him chime in. >> I am OK with either way even no flush way here is more efficient for >> arm64. Let's wait for Minchan's comment. > > Yes, and I don't think there would be any "negative" consequences > without tlb flushes when clearing the A-bit. > >>> If we do end up with ptep_clear_young_notify(), please remove >>> mmu_gather -- it should have been done in this patch. >> >> I suppose "remove mmu_gather" means to trigger flush tlb operation in >> batched way to make sure no stale data in TLB for long time on arm64 >> platform. > > In madvise_cold_or_pageout_pte_range(), we only need struct > mmu_gather *tlb because of tlb_remove_pmd_tlb_entry(), i.e., flushing > tlb after clearing the A-bit. There is no correction, e.g., potential > data corruption, involved there. >From https://lore.kernel.org/lkml/20181029105515.GD14127@arm.com/, the reason that arm64 didn't drop whole flush tlb in ptep_clear_flush_young() is to prevent the stale data in TLB. I suppose there is no correction issue there also. So why keep stale data in TLB in madvise_cold_or_pageout_pte_range() is fine? Regards Yin, Fengwei