From nobody Thu Apr 9 12:50:24 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C66C13A4F2D for ; Mon, 9 Mar 2026 11:55:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773057356; cv=none; b=Fc7kgTEEkxZmGBZuHioz18WRrdUzoumkiWRTpVcrIPeJJHazRLSkdBq0DzTKyEI8ZDF9RoaWIErKPv5L2VW3fADPSjvzBbFv4Fs1/6Cls25OJ6rlb7QOVDYTLEPr1oeI1NN4yca/+fFWnlTS91ki60mtseCwJwDVQcpYgSPXVBc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773057356; c=relaxed/simple; bh=3Y8n25DOYo0e+ho5griIfe1BRl4kOFl+j4nscLRC4B8=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=GrdVK4TNxBD3gK+acsfdabDfdaQS4mslredOv4VnLflxyC3SQdKombvBoRx0DnHnCNUbsAQ1y7iGDeT98nH8LqRO36kl9M0df0K1XX1qdZgDFlDlQJ9xg4lUINV86n5thmD1kBES8W07TK95+yLYczo6q5jIoGhnvysVq7zeJr4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JzmisWH2; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JzmisWH2" Received: by smtp.kernel.org (Postfix) with ESMTPS id 89907C2BC9E; Mon, 9 Mar 2026 11:55:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773057356; bh=3Y8n25DOYo0e+ho5griIfe1BRl4kOFl+j4nscLRC4B8=; h=From:Date:Subject:References:In-Reply-To:To:Cc:Reply-To:From; b=JzmisWH2aRfp/caW061bFd6BhZ9DvkEet1qZK1U1ldiBolCA97Y5vrvrGjBZucCvp MEulNMLz1/OgsQgnFuh90yVa0Wx0L5fc/c3n4HbwA8/Xwat8e9bn+mdmfdgsFISTvM wR+NNhOzIvpb0iX0QgnHob8lJbizCpF6KTQtXl0q0e6pAN+iObQj0SxKkfZ449b25x L3duVqLuLiFyTVo9wSUrl2ZiCV3j2eqNQzAFC13bB5c8uSYaTij9Pg0XMEwh0wiP7j oVDgVEaAsKAT9VsMjNh47VXfGu9SkdEVKxNGog9C2O+9b70ceYvM440iK/g0jNhTrq Bd1qmcPeilagg== Received: from aws-us-west-2-korg-lkml-1.web.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D6F1EFCD9D; Mon, 9 Mar 2026 11:55:56 +0000 (UTC) From: Shivam Kalra via B4 Relay Date: Mon, 09 Mar 2026 17:25:46 +0530 Subject: [PATCH v3 2/2] mm/vmalloc: free unused pages on vrealloc() shrink Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260309-vmalloc-shrink-v3-2-5590fd8de2eb@zohomail.in> References: <20260309-vmalloc-shrink-v3-0-5590fd8de2eb@zohomail.in> In-Reply-To: <20260309-vmalloc-shrink-v3-0-5590fd8de2eb@zohomail.in> To: Andrew Morton , Uladzislau Rezki Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alice Ryhl , Danilo Krummrich , Shivam Kalra X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1773057354; l=2543; i=shivamkalra98@zohomail.in; s=20260212; h=from:subject:message-id; bh=Y6w6SdmqyOX+lKwpSwN3cQqWUNCycwjirQc9nEik+Gw=; b=L/WqM1MJYwB7vVbM9AOGxxZTpnHqTAxqZxh0e6lKXHQvPLuZXyjB0b+6gFXrLrBkH/mTyqQkL aS9B5mwSnayA6paU3NhhXeQ9aA0U2x05yDdAvgHLU3Oya8ycfErgZZd X-Developer-Key: i=shivamkalra98@zohomail.in; a=ed25519; pk=9Q+S1LD/xjbjL7bEaLIlwRADBwU/6LJq7lYm8LFrkQE= X-Endpoint-Received: by B4 Relay for shivamkalra98@zohomail.in/20260212 with auth_id=633 X-Original-From: Shivam Kalra Reply-To: shivamkalra98@zohomail.in From: Shivam Kalra When vrealloc() shrinks an allocation and the new size crosses a page boundary, unmap and free the tail pages that are no longer needed. This reclaims physical memory that was previously wasted for the lifetime of the allocation. The heuristic is simple: always free when at least one full page becomes unused. Huge page allocations (page_order > 0) are skipped, as partial freeing would require splitting. The virtual address reservation (vm->size / vmap_area) is intentionally kept unchanged, preserving the address for potential future grow-in-place support. Fix the grow-in-place check to compare against vm->nr_pages rather than get_vm_area_size(), since the latter reflects the virtual reservation which does not shrink. Without this fix, a grow after shrink would access freed pages. Signed-off-by: Shivam Kalra --- mm/vmalloc.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 42ae68450a90..114e0bd1030e 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -4344,14 +4344,23 @@ void *vrealloc_node_align_noprof(const void *p, siz= e_t size, unsigned long align goto need_realloc; } =20 - /* - * TODO: Shrink the vm_area, i.e. unmap and free unused pages. What - * would be a good heuristic for when to shrink the vm_area? - */ if (size <=3D old_size) { + unsigned int new_nr_pages =3D PAGE_ALIGN(size) >> PAGE_SHIFT; + /* Zero out "freed" memory, potentially for future realloc. */ if (want_init_on_free() || want_init_on_alloc(flags)) memset((void *)p + size, 0, old_size - size); + + /* Free tail pages when shrink crosses a page boundary. */ + if (new_nr_pages < vm->nr_pages && !vm_area_page_order(vm)) { + unsigned long addr =3D (unsigned long)p; + + vunmap_range(addr + (new_nr_pages << PAGE_SHIFT), + addr + (vm->nr_pages << PAGE_SHIFT)); + + vmalloc_free_pages(vm, new_nr_pages, vm->nr_pages); + vm->nr_pages =3D new_nr_pages; + } vm->requested_size =3D size; kasan_vrealloc(p, old_size, size); return (void *)p; @@ -4360,7 +4369,7 @@ void *vrealloc_node_align_noprof(const void *p, size_= t size, unsigned long align /* * We already have the bytes available in the allocation; use them. */ - if (size <=3D alloced_size) { + if (size <=3D (size_t)vm->nr_pages << PAGE_SHIFT) { /* * No need to zero memory here, as unused memory will have * already been zeroed at initial allocation time or during --=20 2.43.0