Re: [PATCH 1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock
On Sun, Jan 21, 2024 at 11:38 PM Suren Baghdasaryan wrote: > > On Sat, Jan 20, 2024 at 1:15 PM Russell King (Oracle) > wrote: > > > > On Sat, Jan 20, 2024 at 09:09:47PM +, > > patchwork-bot+linux-ri...@kernel.org wrote: > > > Hello: > > > > > > This patch was applied to riscv/linux.git (fixes) > > > by Andrew Morton : > > > > > > On Tue, 26 Dec 2023 13:46:10 -0800 you wrote: > > > > A test [1] in Android test suite started failing after [2] was merged. > > > > It turns out that after handling a major fault under per-VMA lock, the > > > > process major fault counter does not register that fault as major. > > > > Before [2] read faults would be done under mmap_lock, in which case > > > > FAULT_FLAG_TRIED flag is set before retrying. That in turn causes > > > > mm_account_fault() to account the fault as major once retry completes. > > > > With per-VMA locks we often retry because a fault can't be handled > > > > without locking the whole mm using mmap_lock. Therefore such retries > > > > do not set FAULT_FLAG_TRIED flag. This logic does not work after [2] > > > > because we can now handle read major faults under per-VMA lock and > > > > upon retry the fact there was a major fault gets lost. Fix this by > > > > setting FAULT_FLAG_TRIED after retrying under per-VMA lock if > > > > VM_FAULT_MAJOR was returned. Ideally we would use an additional > > > > VM_FAULT bit to indicate the reason for the retry (could not handle > > > > under per-VMA lock vs other reason) but this simpler solution seems > > > > to work, so keeping it simple. > > > > > > > > [...] > > > > > > Here is the summary with links: > > > - [1/1] arch/mm/fault: fix major fault accounting when retrying under > > > per-VMA lock > > > https://git.kernel.org/riscv/c/46e714c729c8 > > > > > > You are awesome, thank you! > > > > Now that 32-bit ARM has support for the per-VMA lock, does that also > > need to be patched? > > Yes, I think so. I missed the ARM32 change that added support for > per-VMA locks. Will post a similar patch for it tomorrow. Fix for ARM posted at https://lore.kernel.org/all/20240123064305.2829244-1-sur...@google.com/ > Thanks, > Suren. > > > > > -- > > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > > FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
Re: [PATCH 1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock
On Sat, Jan 20, 2024 at 1:15 PM Russell King (Oracle) wrote: > > On Sat, Jan 20, 2024 at 09:09:47PM +, > patchwork-bot+linux-ri...@kernel.org wrote: > > Hello: > > > > This patch was applied to riscv/linux.git (fixes) > > by Andrew Morton : > > > > On Tue, 26 Dec 2023 13:46:10 -0800 you wrote: > > > A test [1] in Android test suite started failing after [2] was merged. > > > It turns out that after handling a major fault under per-VMA lock, the > > > process major fault counter does not register that fault as major. > > > Before [2] read faults would be done under mmap_lock, in which case > > > FAULT_FLAG_TRIED flag is set before retrying. That in turn causes > > > mm_account_fault() to account the fault as major once retry completes. > > > With per-VMA locks we often retry because a fault can't be handled > > > without locking the whole mm using mmap_lock. Therefore such retries > > > do not set FAULT_FLAG_TRIED flag. This logic does not work after [2] > > > because we can now handle read major faults under per-VMA lock and > > > upon retry the fact there was a major fault gets lost. Fix this by > > > setting FAULT_FLAG_TRIED after retrying under per-VMA lock if > > > VM_FAULT_MAJOR was returned. Ideally we would use an additional > > > VM_FAULT bit to indicate the reason for the retry (could not handle > > > under per-VMA lock vs other reason) but this simpler solution seems > > > to work, so keeping it simple. > > > > > > [...] > > > > Here is the summary with links: > > - [1/1] arch/mm/fault: fix major fault accounting when retrying under > > per-VMA lock > > https://git.kernel.org/riscv/c/46e714c729c8 > > > > You are awesome, thank you! > > Now that 32-bit ARM has support for the per-VMA lock, does that also > need to be patched? Yes, I think so. I missed the ARM32 change that added support for per-VMA locks. Will post a similar patch for it tomorrow. Thanks, Suren. > > -- > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
Re: [PATCH 1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock
On Sat, Jan 20, 2024 at 09:09:47PM +, patchwork-bot+linux-ri...@kernel.org wrote: > Hello: > > This patch was applied to riscv/linux.git (fixes) > by Andrew Morton : > > On Tue, 26 Dec 2023 13:46:10 -0800 you wrote: > > A test [1] in Android test suite started failing after [2] was merged. > > It turns out that after handling a major fault under per-VMA lock, the > > process major fault counter does not register that fault as major. > > Before [2] read faults would be done under mmap_lock, in which case > > FAULT_FLAG_TRIED flag is set before retrying. That in turn causes > > mm_account_fault() to account the fault as major once retry completes. > > With per-VMA locks we often retry because a fault can't be handled > > without locking the whole mm using mmap_lock. Therefore such retries > > do not set FAULT_FLAG_TRIED flag. This logic does not work after [2] > > because we can now handle read major faults under per-VMA lock and > > upon retry the fact there was a major fault gets lost. Fix this by > > setting FAULT_FLAG_TRIED after retrying under per-VMA lock if > > VM_FAULT_MAJOR was returned. Ideally we would use an additional > > VM_FAULT bit to indicate the reason for the retry (could not handle > > under per-VMA lock vs other reason) but this simpler solution seems > > to work, so keeping it simple. > > > > [...] > > Here is the summary with links: > - [1/1] arch/mm/fault: fix major fault accounting when retrying under > per-VMA lock > https://git.kernel.org/riscv/c/46e714c729c8 > > You are awesome, thank you! Now that 32-bit ARM has support for the per-VMA lock, does that also need to be patched? -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
Re: [PATCH 1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock
Hello: This patch was applied to riscv/linux.git (fixes) by Andrew Morton : On Tue, 26 Dec 2023 13:46:10 -0800 you wrote: > A test [1] in Android test suite started failing after [2] was merged. > It turns out that after handling a major fault under per-VMA lock, the > process major fault counter does not register that fault as major. > Before [2] read faults would be done under mmap_lock, in which case > FAULT_FLAG_TRIED flag is set before retrying. That in turn causes > mm_account_fault() to account the fault as major once retry completes. > With per-VMA locks we often retry because a fault can't be handled > without locking the whole mm using mmap_lock. Therefore such retries > do not set FAULT_FLAG_TRIED flag. This logic does not work after [2] > because we can now handle read major faults under per-VMA lock and > upon retry the fact there was a major fault gets lost. Fix this by > setting FAULT_FLAG_TRIED after retrying under per-VMA lock if > VM_FAULT_MAJOR was returned. Ideally we would use an additional > VM_FAULT bit to indicate the reason for the retry (could not handle > under per-VMA lock vs other reason) but this simpler solution seems > to work, so keeping it simple. > > [...] Here is the summary with links: - [1/1] arch/mm/fault: fix major fault accounting when retrying under per-VMA lock https://git.kernel.org/riscv/c/46e714c729c8 You are awesome, thank you! -- Deet-doot-dot, I am a bot. https://korg.docs.kernel.org/patchwork/pwbot.html
