From mboxrd@z Thu Jan 1 00:00:00 1970 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 1B8F238422F; Wed, 8 Jul 2026 22:12:53 +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=1783548774; cv=none; b=Ymdm0liQnbvaI3LYfw9PV49y7YvQBomzdoMxRAvs6NObAefCDYMZdua7va5C0AeZfY30BuusOKVPC5pa/prAEnlYgfbRswEbYxkykIanX7oF2KQU+mHIgxtbDd4oOIRxUD7RaspQjHpgE9L7bb4e0pVlUE49R/hQ/ONVXQB4OGM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783548774; c=relaxed/simple; bh=eXsEHbluTYgc7Mz3d21k+gIlqNoyNr+3C2JAEcsRXmE=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=B43J9xZ/TYJOlcbw9mY0evRUHI5Acjqd42EsmM6OO8uglbcTlZSpBpMYDHWy3qvxfd6l0Y1qTMBeJhQd1o0s34jKs0Yf3gB9iM7q2AB604VOGW3mUhLU9dPqKjGjZHd8Ips0sN0hcFHjQKtgPoasYZ7SLnIZ1e4UXM7SWV6gzl0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MV3qXBxW; 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="MV3qXBxW" Received: by smtp.kernel.org (Postfix) with ESMTPS id C36BEC2BCC7; Wed, 8 Jul 2026 22:12:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1783548773; bh=eXsEHbluTYgc7Mz3d21k+gIlqNoyNr+3C2JAEcsRXmE=; h=From:Date:Subject:References:In-Reply-To:To:Cc:Reply-To:From; b=MV3qXBxWwmiOTBsE+c1lHFSjDqrfTU+ljmCSKBsSiS2+M93IisMEW/VYNSMNROlV9 anZTcjtJ8zgWLH/1lYVpIeDDvFSwKH5ZsiM52EcuHKD76IQrwCNRdMq6MDXbVuG8Pp oSF+6bO3ikXTyobQrKrBAJgPgz4Wz2tT01qx/Zpjgm1yXVEM//mwRDouP7kknyu0lX MZrm9XuBQKWT73EmJqTi+Cy9hugYJKR6HFyCbPnW5ln1jCr8LK9VSIo25TX3DMSQWr +5m/mGp74elvMbj0orQ5O60K4JCYOZ9qiMdZseJCMfJYr3b0JQszOKyciqeLUExswr SKlGqsXBFQVlg== 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 A702CC44501; Wed, 8 Jul 2026 22:12:53 +0000 (UTC) From: Ackerley Tng via B4 Relay Date: Wed, 08 Jul 2026 15:12:49 -0700 Subject: [PATCH v2 1/5] mm: hugetlb: Track used_hpages when getting/putting pages from subpool 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: 7bit Message-Id: <20260708-hugetlb-alloc-failure-fixes-v2-1-c7f27cbb462b@google.com> References: <20260708-hugetlb-alloc-failure-fixes-v2-0-c7f27cbb462b@google.com> In-Reply-To: <20260708-hugetlb-alloc-failure-fixes-v2-0-c7f27cbb462b@google.com> To: Muchun Song , Oscar Salvador , David Hildenbrand , Joshua Hahn , Shakeel Butt , Nhat Pham , Andrew Morton , Peter Xu , Wupeng Ma , fvdl@google.com, rientjes@google.com, jthoughton@google.com Cc: vannapurve@google.com, erdemaktas@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ackerley Tng , stable@vger.kernel.org X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1783548773; l=6331; i=ackerleytng@google.com; s=20260225; h=from:subject:message-id; bh=Qs4eCEk5U9LKKEAxFUKXDcH5Rd3MYbOxpQQpyCVKVJM=; b=PB/EsnDjFkR0V2Vg0gbj6SlXlDr09cVBrcs109h50qBtLspPgKcGqeqJCE56lt3SnXM5z0Itq LMqGdHf3patDG6iCECkmbw+lsy4uB87heVsS8npJX/6DVo7AY+URCUg X-Developer-Key: i=ackerleytng@google.com; a=ed25519; pk=sAZDYXdm6Iz8FHitpHeFlCMXwabodTm7p8/3/8xUxuU= X-Endpoint-Received: by B4 Relay for ackerleytng@google.com/20260225 with auth_id=649 X-Original-From: Ackerley Tng Reply-To: ackerleytng@google.com From: Ackerley Tng hugepage_subpool_put_pages() currently has two distinct responsibilities that conflict: 1. When size is specified for the mount, max_hpages != -1: Keep track of total active pages (allocated + reserved) and decrement this count (used_hpages) when a page is freed or allocation fails. 2. When min_size is specified for the mount, min_hpages != -1: Ensure we don't drop below the guaranteed minimum, and restore a reservation (rsv_hpages) if we do. This causes trouble because when allocation fails (refer to alloc_hugetlb_folio()) if gbl_chg = 1 (i.e. no subpool reservation was taken): + To keep used_hpages consistent, HugeTLB needs to call hugepage_subpool_put_pages() to restore undo used_hpages being incremented + But can't call hugepage_subpool_put_pages() if no reservation was consumed. One option would be to conditionally do subpool tracking updates outside of the hugepage_subpool_put_pages() function, but that would spread logic all over. Instead, always track used_hpages, regardless of whether a max_size was requested for the mount, so that the subpool always knows how many pages were allocated through it. Every page allocated through the subpool increments used_hpages, regardless of whether a reservation was taken from it. Conceptually, now, every allocation involving a subpool uses a page from the subpool, which must be returned to the subpool. Every page taken from the subpool tries to use a subpool reservation. Restoring a page to the subpool reservations only if the page was taken from subpool reservations. (If used_hpages >= min_hpages, the page must have not have been taken from the reservations.) Always tracking used_hpages provides the subpool with information of both used and reserved counts to make the correct decision for both max_size and min_size correctly. With used_hpages always tracked, subpool_is_free() can be simplified, such that the subpool can be declared free if there are no more pages in use. Also update the documentation for used_hpages, since it no longer matters whether the used pages count against the maximum. Also update statfs reporting. Previously, if max_hpages is negative, used_hpages is static at 0, so returning max_hpages - used_hpages returns -1 and is always correct. Now, if the subpool doesn't have a maximum requested size, indicate no limit for free pages (-1). If it does have a maximum size, report the difference between the requested size and the number of used pages. This difference is always positive, because if the mount does have a maximum size, hugepage_subpool_get_pages() ensures that the subpool usage never exceeds the maximum. This fixes a bug in hugetlb_unreserve_pages(), where pages are returned to the subpool regardless of whether it consumed a reservation. The corresponding bug in the failure handling path of alloc_hugetlb_folio() was fixed in a833a693a490e. Fixes: 1c5ecae3a93fa ("hugetlbfs: add minimum size accounting to subpools") Cc: stable@vger.kernel.org Signed-off-by: Ackerley Tng --- fs/hugetlbfs/inode.c | 8 ++++++-- include/linux/hugetlb.h | 4 ++-- mm/hugetlb.c | 22 ++++++++-------------- 3 files changed, 16 insertions(+), 18 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 216e1a0dd0b23..26c0187340636 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -1109,8 +1109,12 @@ static int hugetlbfs_statfs(struct dentry *dentry, struct kstatfs *buf) spin_lock_irq(&sbinfo->spool->lock); buf->f_blocks = sbinfo->spool->max_hpages; - free_pages = sbinfo->spool->max_hpages - - sbinfo->spool->used_hpages; + if (sbinfo->spool->max_hpages == -1) { + free_pages = -1; + } else { + free_pages = sbinfo->spool->max_hpages - + sbinfo->spool->used_hpages; + } buf->f_bavail = buf->f_bfree = free_pages; spin_unlock_irq(&sbinfo->spool->lock); buf->f_files = sbinfo->max_inodes; diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 2abaf99321e90..34b9a3e1be0fa 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -38,8 +38,8 @@ struct hugepage_subpool { spinlock_t lock; long count; long max_hpages; /* Maximum huge pages or -1 if no maximum. */ - long used_hpages; /* Used count against maximum, includes */ - /* both allocated and reserved pages. */ + long used_hpages; /* Used page count, includes both */ + /* allocated and reserved pages. */ struct hstate *hstate; long min_hpages; /* Minimum huge pages or -1 if no minimum. */ long rsv_hpages; /* Pages reserved against global pool to */ diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 571212b80835e..ee5e99c1894b9 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -129,12 +129,8 @@ static inline bool subpool_is_free(struct hugepage_subpool *spool) { if (spool->count) return false; - if (spool->max_hpages != -1) - return spool->used_hpages == 0; - if (spool->min_hpages != -1) - return spool->rsv_hpages == spool->min_hpages; - return true; + return spool->used_hpages == 0; } static inline void unlock_or_release_subpool(struct hugepage_subpool *spool, @@ -205,15 +201,14 @@ static long hugepage_subpool_get_pages(struct hugepage_subpool *spool, spin_lock_irq(&spool->lock); - if (spool->max_hpages != -1) { /* maximum size accounting */ - if ((spool->used_hpages + delta) <= spool->max_hpages) - spool->used_hpages += delta; - else { - ret = -ENOMEM; - goto unlock_ret; - } + if (spool->max_hpages != -1 && + spool->used_hpages + delta > spool->max_hpages) { + ret = -ENOMEM; + goto unlock_ret; } + spool->used_hpages += delta; + /* minimum size accounting */ if (spool->min_hpages != -1 && spool->rsv_hpages) { if (delta > spool->rsv_hpages) { @@ -251,8 +246,7 @@ static long hugepage_subpool_put_pages(struct hugepage_subpool *spool, spin_lock_irqsave(&spool->lock, flags); - if (spool->max_hpages != -1) /* maximum size accounting */ - spool->used_hpages -= delta; + spool->used_hpages -= delta; /* minimum size accounting */ if (spool->min_hpages != -1 && spool->used_hpages < spool->min_hpages) { -- 2.55.0.795.g602f6c329a-goog