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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 78F63A000C X-Stat-Signature: xeupo5ntmqoe7i3xs36f5otzihbcte9w X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1753448910-725904 X-HE-Meta: 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 f6K+PThM 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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 25.07.25 00:27, Usama Arif wrote: > >> Hi! >> >>> >>> Over here, with MMF_DISABLE_THP_EXCEPT_ADVISED, MADV_HUGEPAGE will succeed as vm_flags has >>> VM_HUGEPAGE set, but MADV_COLLAPSE will fail to give a hugepage (as VM_HUGEPAGE is not set >>> and MMF_DISABLE_THP_EXCEPT_ADVISED is set) which I feel might not be the right behaviour >>> as MADV_COLLAPSE is "advise" and the prctl flag is PR_THP_DISABLE_EXCEPT_ADVISED? >> >> THPs are disabled for these regions, so it's at least consistent with the "disable all", but ... >> >>> >>> This will be checked in multiple places in madvise_collapse: thp_vma_allowable_order, >>> hugepage_vma_revalidate which calls thp_vma_allowable_order and hpage_collapse_scan_pmd >>> which also ends up calling hugepage_vma_revalidate. >>>> A hacky way would be to save and overwrite vma->vm_flags with VM_HUGEPAGE at the start of madvise_collapse >>> if VM_NOHUGEPAGE is not set, and reset vma->vm_flags to its original value at the end of madvise_collapse >>> (Not something I am recommending, just throwing it out there). >> >> Gah. >> >>> >>> Another possibility is to pass the fact that you are in madvise_collapse to these functions >>> as an argument, this might look ugly, although maybe not as ugly as hugepage_vma_revalidate >>> already has collapse control arg, so just need to take care of thp_vma_allowable_orders. >> >> Likely this. >> >>> >>> Any preference or better suggestions? >> >> What you are asking for is not MMF_DISABLE_THP_EXCEPT_ADVISED as I planned it, but MMF_DISABLE_THP_EXCEPT_ADVISED_OR_MADV_COLLAPSE. >> >> Now, one could consider MADV_COLLAPSE an "advise". (I am not opposed to that change) >> > > lol yeah I always think of MADV_COLLAPSE as an extreme version of MADV_HUGE (more of a demand > than an advice :)), eventhough its not persistant. > Which is why I think might be unexpected if MADV_HUGE gives hugepages but MADV_COLLAPSE doesn't > (But could just be my opinion). > >> Indeed, the right way might be telling vma_thp_disabled() whether we are in collapse. >> >> Can you try implementing that on top of my patch to see how it looks? >> > > My reasoning is that a process that is running with system policy always but with > PR_THP_DISABLE_EXCEPT_ADVISED gets THPs in exactly the same behaviour as a process that is running > with system policy madvise. This will help us achieve (3) that you mentioned in the > commit message: > (3) Switch from THP=madvise to THP=always, but keep the old behavior > (THP only when advised) for selected workloads. > > > I have written quite a few selftests now for prctl SET_THP_DISABLE, both with and without > PR_THP_DISABLE_EXCEPT_ADVISED set incorporating your feedback on it. I have all of them passing > with the below diff. The diff is slightly ugly, but very simple and hopefully acceptable. If it > looks good, I can send a series with everything. Probably make the below diff as a separate patch > on top of this patch as its mostly adding an extra arg to functions and would keep the review easier? Yes, we should do it as a separate patch, makes our life easier, because that requires more work. We require a cleanup first, the boolean parameter for __thp_vma_allowable_orders() is no good. I just pushed something untested to my branch (slightly adjusted patch#1 + 2 more patches), can you have a look at that? (untested ... :) ) -- Cheers, David / dhildenb