From nobody Wed Apr 15 16:48:38 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 A8A8C3B3C00 for ; Wed, 4 Mar 2026 14:53:29 +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=1772636009; cv=none; b=S8a86jXFk60DrinZuQKtNkolfyNmVKLigH8+ZK50TGULgK2xfed6zYwcNY3WXmnZXQAQsauji7Ko8UYxZI9tnl2MWe5GJ5fl8lEGn4YXpilDsko+9TBFi//7muVgwpB87nfVId9geOkUqWftCMFydcqS5rhnVEJuMp5S3sibCSY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772636009; c=relaxed/simple; bh=obzS9P6ZNeJAxn5nItDpGm+ktrhNRXvYN4TD1fyB2FU=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=DL28KzlBiZS7mkQAHZqqYPTP32ArUmIMbMD9w61V55ZfLVUN6vRTD9PaV7y2pQryMO9P6J96XIdDalsE9vM4Tq9krcxDrYkb60oMQPnbK82trnD14j7gZ1mLti1Qqavj3CaOYrIoHz+MIHTBUUSKkMZFCQ7oC1AI+8+o6SsCzdA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Im4hCNPI; 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="Im4hCNPI" Received: by smtp.kernel.org (Postfix) with ESMTPS id 88F79C2BC9E; Wed, 4 Mar 2026 14:53:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772636009; bh=obzS9P6ZNeJAxn5nItDpGm+ktrhNRXvYN4TD1fyB2FU=; h=From:Date:Subject:References:In-Reply-To:To:Cc:Reply-To:From; b=Im4hCNPIosrXVQBGxE8Ipsea7tdG4rpM+qk85retlt2KiOKccGzRdu3+pAw9dMYXm +ZW9ZBRcatAzi6hTwksmnvsHx8RrvWW8fMqgBrPOrW7r6N/WBOUyrbog5b3rN6BcjS QOrq1XW8T1SnvDo9AjlMve2hFwnoJSgsF0UwzXs1YjYb9TShUuiApiQUL0Gm7H7H8v O4Ep4XwnCVaBkBy0fQQDEZnocobohWIFwvZSN/SRdGY9+1ea03FdC3uIk/6r81ASh7 Nrkps7DkZVSrZYwL7V8jRaGwRcd3/BOW/IO1acL0IqaTJBY5F0MhddYz26GFTz+8/e 63SxP1kXEDN8Q== 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 7CA5CEF8FF3; Wed, 4 Mar 2026 14:53:29 +0000 (UTC) From: Shivam Kalra via B4 Relay Date: Wed, 04 Mar 2026 20:23:16 +0530 Subject: [PATCH v2 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: <20260304-vmalloc-shrink-v2-2-28c291d60100@zohomail.in> References: <20260304-vmalloc-shrink-v2-0-28c291d60100@zohomail.in> In-Reply-To: <20260304-vmalloc-shrink-v2-0-28c291d60100@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=1772636006; l=2543; i=shivamkalra98@zohomail.in; s=20260212; h=from:subject:message-id; bh=OKQH3IWxL4ounbCE+6VgaXMjPoT4ux/8tD8AGU1gTJo=; b=XNA3+LeXRJL7O5ATYcsa+KLREiMcLDVQS5J9AI3I7lUZGevOoDDdscBLtWr+7Zg0rAx2tNSCN h50igQWgwQOD+lDRnPxcaWkq3mCXBLTeE2qV6mz8HTdO/zdrWXnwTgZ 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 e2aef0a79f2e..1a59afb94ba4 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -4340,14 +4340,23 @@ 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; @@ -4356,7 +4365,7 @@ 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