From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f74.google.com (mail-wm1-f74.google.com [209.85.128.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2EEFC3264CE for ; Tue, 14 Apr 2026 16:57:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776185879; cv=none; b=U9KSoEYyf9JLTNe6WkXwimiIaOMkNhcFsXpJa7wFD1e9zLgaLEJwh+94QLMcWXCoYTNqHyerZs6acVL6ScPhxT9Ecx7gNxy9rjDib6FG9sF1L5XosjonUh53WB2rq5wSR78eIi9awHwyZ0zKoTx7grFBOEP1TPhUo0NdEnUOPEk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776185879; c=relaxed/simple; bh=Y/BgDh/47SbNVflJYhLVGAcPoNx1RkF2s6BSFno1Kq4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=ieDJKnImyh5SaztKMcwuUCl0AvOlrBfOTzTVhlpSPcnmRMq5s48T96RpiH+fBckpNBcnm8sPzDqX0l8aEt1y+kg5cI+7+fMZEYvyZ5IwUtISO890uPOlqGjuzSXg+KzWbaj6quJ27i50ZUfYXOwkRWM+65vxogAI3dIZ0F6EcOA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--aliceryhl.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=dQLB/5d2; arc=none smtp.client-ip=209.85.128.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--aliceryhl.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="dQLB/5d2" Received: by mail-wm1-f74.google.com with SMTP id 5b1f17b1804b1-488e097a270so20696575e9.1 for ; Tue, 14 Apr 2026 09:57:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1776185877; x=1776790677; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=UkYGbEc6QvWyzB+ejatgY30VNPQeVmDmmsT64e5J5sc=; b=dQLB/5d2sMMzG+JtmJFjAkRUCi9KaKypkhwzzxH6WwKUmWWU27lfZmKwLKbNcyuhEg xwnTKIxovnJMzur86n2Ja8tL70b7wCPw10bwwSeWMvNai64C2bM25a+4omqkEjssHYlO PHxnGKH79/0f/6+vrZh42y14LDWI22sgD2VVvTlI9vNP73bF7OJeEWn5LPgdwDyA6Ttp m2cHhALoYfBs/eRSjKHeLT/vcMai36JXgqOq/qnBUgi2U0zBDBuH+wda1pQ/JPbqdlXr GuEeZ054TTPjlFfgI3MeaxeTIsFlHxKDLjjvdTmetzZlK87mmtf3OYyHHA6dZbKSrTNK hmYQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776185877; x=1776790677; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=UkYGbEc6QvWyzB+ejatgY30VNPQeVmDmmsT64e5J5sc=; b=IZlIVZfXz95uJ4ZXNrSJTtq7O1qRE5v3gpVmfimuAAiftJRxr/k7NxtzzeszId8SXS gkWBRDs9pyba4m2Ul17JSe8d9AGceDeIbFOw0t2oXqz3MEk6c/L1YahZzsvwjbWgftrv cpmvP6s7fAArum/p/NWzfwoquufCOjbp0im9yN+5LvKyniu/Fq7c6tblKoIWePaYqOg7 cOs1uMnz9XV+AZX2h56Aa3LeHtp7rm0HMx6YXjx5X0VY/qWa23WMD6h4sGm2WrXRn7FS i6Up2VUY6MLvcJ9fdkf/jn685VjfpHQdW3Vw4Mit7Z+T2rVJqL/zQ6+WOhavlzlPy0gB vczw== X-Forwarded-Encrypted: i=1; AFNElJ8fTkL2VoSsozws8NwCsrcrwt4iuOWB2E0PwK6e3JFO0riBBE1kSV0pqzfxZuWNAq73KZ+fOUdNHtZXY6g=@vger.kernel.org X-Gm-Message-State: AOJu0YxmFhyLoJeaWPs1kh7CH5mZGtUUC6G0b3Hlmxntvr8W+Wr0JKSp I1j+PgHh6r/SauftRc3o4B3+USYhLgX0yMIsNOOyO0uJUcVp2Ti3XTHA9R0z6c678xSruDiopuw 3cuWul7OB8YGnPF7Fcg== X-Received: from wrfo7.prod.google.com ([2002:a5d:58c7:0:b0:439:cfa2:e197]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:674f:b0:488:a82f:bb9b with SMTP id 5b1f17b1804b1-488d68cb47amr264888155e9.30.1776185876348; Tue, 14 Apr 2026 09:57:56 -0700 (PDT) Date: Tue, 14 Apr 2026 16:57:55 +0000 In-Reply-To: <7d16f260-ffd0-4e45-b66e-9e7f71332466@zohomail.in> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260404-vmalloc-shrink-v10-0-335759165dfa@zohomail.in> <7d16f260-ffd0-4e45-b66e-9e7f71332466@zohomail.in> Message-ID: Subject: Re: [PATCH v10 0/4] mm/vmalloc: free unused pages on vrealloc() shrink From: Alice Ryhl To: Shivam Kalra Cc: Andrew Morton , Uladzislau Rezki , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Danilo Krummrich Content-Type: text/plain; charset="utf-8" On Tue, Apr 14, 2026 at 02:09:09PM +0530, Shivam Kalra wrote: > On 04/04/26 14:06, Shivam Kalra via B4 Relay wrote: > > This series implements the TODO in vrealloc() to unmap and free unused > > pages when shrinking across a page boundary. > > > > Problem: > > When vrealloc() shrinks an allocation, it updates bookkeeping > > (requested_size, KASAN shadow) but does not free the underlying physical > > pages. This wastes memory for the lifetime of the allocation. > > > > Solution: > > - Patch 1: Extracts a vm_area_free_pages(vm, start_idx, end_idx) helper > > from vfree() that frees a range of pages with memcg and nr_vmalloc_pages > > accounting. Freed page pointers are set to NULL to prevent stale > > references. > > - Patch 2: Update the grow-in-place check in vrealloc() to compare the > > requested size against the actual physical page count (vm->nr_pages) > > rather than the virtual area sizes. This is a prerequisite for shrinking. > > - Patch 3: Uses the helper to free tail pages when vrealloc() shrinks > > across a page boundary. > > - Patch 4: Adds a vrealloc test case to lib/test_vmalloc that exercises > > grow-realloc, shrink-across-boundary, shrink-within-page, and > > grow-in-place paths. > > > > The virtual address reservation is kept intact to preserve the range > > for potential future grow-in-place support. > > A concrete user is the Rust binder driver's KVVec::shrink_to [1], which > > performs explicit vrealloc() shrinks for memory reclamation. > > > > Tested: > > - KASAN KUnit (vmalloc_oob passes) > > - lib/test_vmalloc stress tests (3/3, 1M iterations each) > > - checkpatch, sparse, W=1, allmodconfig, coccicheck clean > > > > [1] https://lore.kernel.org/all/20260216-binder-shrink-vec-v3-v6-0-ece8e8593e53@zohomail.in/ > > > > Suggested-by: Danilo Krummrich > > Signed-off-by: Shivam Kalra > > --- > > Changes in v10: > > - Reorder vm->nr_pages to the beginning (Alice Ryhl) > > - Link to v9: https://lore.kernel.org/r/20260401-vmalloc-shrink-v9-0-bf58dfb997d8@zohomail.in > > > > Changes in v9: > > - Remove READ_ONCE, WRITE_ONCE and drop commit > > about show_numa_info. (Uladzislau Rezki) > > - Update the commit message in Patch 2. (Alice Ryhl) > > - Remove zero newly exposed memory commit. > > - Link to v8: https://lore.kernel.org/r/20260327-vmalloc-shrink-v8-0-cc6b57059ed7@zohomail.in > > > > Changes in v8: > > - Strip the KASAN tag from the pointer before addr_to_node() > > to avoid acquiring the wrong node lock (Sashiko). > > - Rebase to latest mm-new. > > - Link to v7: https://lore.kernel.org/r/20260324-vmalloc-shrink-v7-0-c0e62b8e5d83@zohomail.in > > > > Changes in v7: > > - Fix NULL pointer dereference in shrink path (Sashiko) > > - Acquire vn->busy.lock when updating vm->nr_pages to synchronize > > with concurrent readers (Uladzislau Rezki) > > - Use READ_ONCE in vmalloc_dump_obj (Sashiko) > > - Skip shrink path on GFP_NIO or GFP_NOFS. (Sashiko) > > - Fix Overflow issue for large allocations. (Sashiko) > > - Use vrealloc instead of vmalloc in vrealloc test. > > - Link to v6: https://lore.kernel.org/r/20260321-vmalloc-shrink-v6-0-062ca7b7ceb2@zohomail.in > > > > Changes in v6: > > - Fix VM_USERMAP crash by explicitly bypassing early in the shrink path if the flag is set.(Sashiko) > > - Fix Kmemleak scanner panic by calling kmemleak_free_part() to update tracking on shrink.(Sashiko) > > - Fix /proc/vmallocinfo race condition by protecting vm->nr_pages access with > > READ_ONCE()/WRITE_ONCE() for concurrent readers.(Sashiko) > > - Fix stale data leak on grow-after-shrink by enforcing mandatory zeroing of the newly exposed memory.(Sashiko) > > - Fix memory leaks in vrealloc_test() by using a temporary pointer to preserve and > > free the original allocation upon failure.(Sashiko) > > - Rename vmalloc_free_pages parameters from start/end to start_idx/end_idx for better clarity.(Uladzislau Rezki) > > - Link to v5: https://lore.kernel.org/r/20260317-vmalloc-shrink-v5-0-bbfbf54c5265@zohomail.in > > - Link to Sashiko: https://sashiko.dev/#/patchset/20260317-vmalloc-shrink-v5-0-bbfbf54c5265%40zohomail.in > > > > Changes in v5: > > - Skip vrealloc shrink for VM_FLUSH_RESET_PERMS (Uladzislau Rezki) > > - Link to v4: https://lore.kernel.org/r/20260314-vmalloc-shrink-v4-0-c1e2e0bb5455@zohomail.in > > > > Changes in v4: > > - Rename vmalloc_free_pages() to vm_area_free_pages() to align with > > vm_area_alloc_pages() (Uladzislau Rezki) > > - NULL out freed vm->pages[] entries to prevent stale pointers (Alice Ryhl) > > - Remove redundant if (vm->nr_pages) guard in vfree() (Uladzislau Rezki) > > - Add vrealloc test case to lib/test_vmalloc (new patch 3/3) > > - Link to v3: https://lore.kernel.org/r/20260309-vmalloc-shrink-v3-0-5590fd8de2eb@zohomail.in > > > > Changes in v3: > > - Restore the comment. > > - Rebase to the latest mm-new > > - Link to v2: https://lore.kernel.org/r/20260304-vmalloc-shrink-v2-0-28c291d60100@zohomail.in > > > > Changes in v2: > > - Updated the base-commit to mm-new > > - Fix conflicts after rebase > > - Ran `clang-format` on the changes made > > - Use a single `kasan_vrealloc` (Alice Ryhl) > > - Link to v1: https://lore.kernel.org/r/20260302-vmalloc-shrink-v1-0-46deff465b7e@zohomail.in > > > > --- > > Shivam Kalra (4): > > mm/vmalloc: extract vm_area_free_pages() helper from vfree() > > mm/vmalloc: use physical page count for vrealloc() grow-in-place check > > mm/vmalloc: free unused pages on vrealloc() shrink > > lib/test_vmalloc: add vrealloc test case > > > > lib/test_vmalloc.c | 62 ++++++++++++++++++++++++++++++ > > mm/vmalloc.c | 111 ++++++++++++++++++++++++++++++++++++++++++++--------- > > 2 files changed, 154 insertions(+), 19 deletions(-) > > --- > > base-commit: b47b4fa4c232ee36aae58630e9d6520e35d33f3a > > change-id: 20260302-vmalloc-shrink-04b2fa688a14 > > > > Best regards, > Hey Ulad, Andrew > A gentle thread bump. Will we include this in this merge window? > Let me know if you have any suggestions, I will resolve them > asap. If you mean the merge window that opened yesterday, then it's too late for that, and I believe we agreed to not include it there anyway in [1]. I can try to look at it again. I guess the main difficult thing is interactions with other parts of the kernel, of which sashiko claims to have found another one [2]. I can't help but wonder if it would be better to reduce the vma size to avoid issues with other codepaths using get_vm_area_size(vm) and assuming that all pages in that range are mapped. [1]: https://lore.kernel.org/lkml/20260327113758.75f04588310a707b4d4b1aac@linux-foundation.org/ [2]: https://sashiko.dev/#/patchset/20260404-vmalloc-shrink-v10-0-335759165dfa%40zohomail.in