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a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1707861473; x=1708466273; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=ir4+0EAbk6DmHSJMCOQ+63RTEjcKM6OBoUCHYQ558Qo=; b=Z2syN5LNhc2RrVTe9Wh5aUgM42WA5VdKdJTmY84ptaaTakQ+cs4Ey/MNDxzMC7fBTV eKysJJJgcHq6/Vckrs/T0ms7yu08hgDyqoYkmLgh4IJUnI/+A+BDuuv4ZHPGiuyV6Wgz SCzYA9zLbFh2+TXaktRIfRDawTsN/RuDXR9uNHu7QcR/4rDvanhKpXIF2ortyeVMIrNE wgiCDxvS0VSLN+qPR2GqIw7KktiFpU/bAJqfHxUwrCiMR1XaSm5aj8zwz2WTBB2HD9WN fMxTMCu+j5SrkDqlbIzaYiGhZX9w4uOZhfleKzle0Oc5ZCPpGLiW+ObD6V47fFzzafq/ 0Icg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1707861473; x=1708466273; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=ir4+0EAbk6DmHSJMCOQ+63RTEjcKM6OBoUCHYQ558Qo=; b=oaiUyrHddDuFkJ0CsL9IQKxAkxAc05xTKRxsxVLP848sI6k2Ly8Cw4F+nhsIVtDs9O ydJ2gri6wzLrWjR2C7bf/L/tDV5ODOZdHzsPg93BP67LtqrbWnHgz+Fq3nKnWo2PTnUu L64vEF0Ur/WREjkSv62fDbUV7VQv4FEW1IQierLyfUZnze5lMIXJSRdEIeObrb26m0zz K1FRPzAiK8lK+pCTCpwhKm6tlqzU/a1TJvYHip7J5OCLFfgG4cq4j33Db6MA3c7WocK+ 9IA+9LKRTWhQ06SAtpQRdOb9xMAKOBB9psmisbq6ZpdPNj1R1vJemwGkSdDojouECltk yRdQ== X-Forwarded-Encrypted: i=1; AJvYcCVUNEeDCA9NuCukPdS1ukTVNrN9HD0FRmiMyUNyiz/tUPJnK1sulFfZkBndUnZWLp4YnZIMNcIH9NTai6vlGM1taHVtYT9XRYyKHcwT2A== X-Gm-Message-State: AOJu0Yy9MqAQUptWWMFU9ncJe0IE8crhT7XmAYzhP98dB3EKNOn/vHae MqOpI5l+Z4aNb2KbpYMEh+C0R8x4eOBSjPG+ehiY1iqdTJ9MN4Lu0yJilHI6EyqfaHNnJlWj/qU Eyd9IPYWjdaeIGrdpQGLrhQ== X-Google-Smtp-Source: AGHT+IFDSd5xu2FB72V4FXpKTmeqW1QesEeAS6gwaRywm0PkcXIJA1oGvUM9nR5x/IAVPoUhZ5UVHHp7Mrodt7B/AA== X-Received: from lg.mtv.corp.google.com ([2620:15c:211:202:ce6c:821f:a756:b4b8]) (user=lokeshgidra job=sendgmr) by 2002:a81:5702:0:b0:5ff:6ec3:b8da with SMTP id l2-20020a815702000000b005ff6ec3b8damr12240ywb.1.1707861473107; Tue, 13 Feb 2024 13:57:53 -0800 (PST) Date: Tue, 13 Feb 2024 13:57:38 -0800 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.43.0.687.g38aa6559b0-goog Message-ID: <20240213215741.3816570-1-lokeshgidra@google.com> Subject: [PATCH v6 0/3] per-vma locks in userfaultfd From: Lokesh Gidra To: akpm@linux-foundation.org Cc: lokeshgidra@google.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, selinux@vger.kernel.org, surenb@google.com, kernel-team@android.com, aarcange@redhat.com, peterx@redhat.com, david@redhat.com, axelrasmussen@google.com, bgeffon@google.com, willy@infradead.org, jannh@google.com, kaleshsingh@google.com, ngeoffray@google.com, timmurray@google.com, rppt@kernel.org, Liam.Howlett@oracle.com Performing userfaultfd operations (like copy/move etc.) in critical section of mmap_lock (read-mode) causes significant contention on the lock when operations requiring the lock in write-mode are taking place concurrently. We can use per-vma locks instead to significantly reduce the contention issue. Android runtime's Garbage Collector uses userfaultfd for concurrent compaction. mmap-lock contention during compaction potentially causes jittery experience for the user. During one such reproducible scenario, we observed the following improvements with this patch-set: - Wall clock time of compaction phase came down from ~3s to <500ms - Uninterruptible sleep time (across all threads in the process) was ~10ms (none in mmap_lock) during compaction, instead of >20s Changes since v5 [5]: - Use abstract function names (like uffd_mfill_lock/uffd_mfill_unlock) to avoid using too many #ifdef's, per Suren Baghdasaryan and Liam Howlett - Use 'unlikely' (as earlier) to anon_vma related checks, per Liam Howlett - Eliminate redundant ptr->err->ptr conversion, per Liam Howlett - Use 'int' instead of 'long' for error return type, per Liam Howlett Changes since v4 [4]: - Fix possible deadlock in find_and_lock_vmas() which may arise if lock_vma() is used for both src and dst vmas. - Ensure we lock vma only once if src and dst vmas are same. - Fix error handling in move_pages() after successfully locking vmas. - Introduce helper function for finding dst vma and preparing its anon_vma when done in mmap_lock critical section, per Liam Howlett. - Introduce helper function for finding dst and src vmas when done in mmap_lock critical section. Changes since v3 [3]: - Rename function names to clearly reflect which lock is being taken, per Liam Howlett. - Have separate functions and abstractions in mm/userfaultfd.c to avoid confusion around which lock is being acquired/released, per Liam Howlett. - Prepare anon_vma for all private vmas, anonymous or file-backed, per Jann Horn. Changes since v2 [2]: - Implement and use lock_vma() which uses mmap_lock critical section to lock the VMA using per-vma lock if lock_vma_under_rcu() fails, per Liam R. Howlett. This helps simplify the code and also avoids performing the entire userfaultfd operation under mmap_lock. Changes since v1 [1]: - rebase patches on 'mm-unstable' branch [1] https://lore.kernel.org/all/20240126182647.2748949-1-lokeshgidra@google.com/ [2] https://lore.kernel.org/all/20240129193512.123145-1-lokeshgidra@google.com/ [3] https://lore.kernel.org/all/20240206010919.1109005-1-lokeshgidra@google.com/ [4] https://lore.kernel.org/all/20240208212204.2043140-1-lokeshgidra@google.com/ [5] https://lore.kernel.org/all/20240213001920.3551772-1-lokeshgidra@google.com/ Lokesh Gidra (3): userfaultfd: move userfaultfd_ctx struct to header file userfaultfd: protect mmap_changing with rw_sem in userfaulfd_ctx userfaultfd: use per-vma locks in userfaultfd operations fs/userfaultfd.c | 86 ++----- include/linux/userfaultfd_k.h | 75 ++++-- mm/userfaultfd.c | 438 +++++++++++++++++++++++++--------- 3 files changed, 405 insertions(+), 194 deletions(-) Reviewed-by: Liam R. Howlett