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 1B564382293 for ; Mon, 18 May 2026 17:54:21 +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=1779126862; cv=none; b=pu0x5zfkjTe0QKGgvrgzRdZj2JBFxoCqCuCgTpuggr1jJ3py3ekQFpb8CcgX9grrP1D45n8D8E6eQqP3NeftU65bhILMKbB290ucppfypr4bq8ugHrc+dbjvbmxnSN92xQqqixHPOr1PfIdjVeL+yArEFflgrKGlOMfezg1OW+o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779126862; c=relaxed/simple; bh=LUsi4sLMcCNJ1TPYR1sl8pKbvelel56d5UGQDYLhhug=; h=Date:To:From:Subject:Message-Id; b=ha39U8WQY6sBTdyO2M/6ka3mH3dyGUM/D1nu4pnVLY8ex0Ieb0lMtNa1lmMZhox6CUiXNQ3f1YdpIbxhtqXoOvkPRSKlF7EEsqmucKhC26nNCJYDu5OU1VP5fIWQ7htY81NkQ/bLiU43KLemvKZa1VWokYKAITM5ZOAqgENL0JU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=v1vRxfjL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="v1vRxfjL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A918EC2BCB7; Mon, 18 May 2026 17:54:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1779126861; bh=LUsi4sLMcCNJ1TPYR1sl8pKbvelel56d5UGQDYLhhug=; h=Date:To:From:Subject:From; b=v1vRxfjLAXdJZzGW2U6mztHahkDMVB98k/o0nkdrCXokrN1y5cu5u3+C6u32vviJT u1T4X+HPdaMmqB65yhy+W/Vhzvxzdz2Z6XYfajQbuDJH8X40rDhhpXf6wsRv59qcwe fa7ElRUjAx7sVDheJzxe1Pt9niPGSbh79asGCR2w= Date: Mon, 18 May 2026 10:54:21 -0700 To: mm-commits@vger.kernel.org,joonwonkang@google.com,akpm@linux-foundation.org From: Andrew Morton Subject: [to-be-updated] percpu-fix-hint-invariant-breakage.patch removed from -mm tree Message-Id: <20260518175421.A918EC2BCB7@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: percpu: fix hint invariant breakage has been removed from the -mm tree. Its filename was percpu-fix-hint-invariant-breakage.patch This patch was dropped because an updated version will be issued ------------------------------------------------------ From: Joonwon Kang Subject: percpu: fix hint invariant breakage Date: Sun, 10 May 2026 07:21:49 +0000 The invariant "scan_hint_start > contig_hint_start if and only if scan_hint == contig_hint" should be kept for hint management. However, it could be broken in some cases: - if (new contig == contig_hint == scan_hint) && (contig_hint_start < scan_hint_start < new contig start) && the new contig is to become a new contig_hint due to its better alignment, then scan_hint should be invalidated instead of keeping the old value. - if (new contig == contig_hint > scan_hint) && (new contig start < contig_hint_start) && the new contig is not to become a new contig_hint, then scan_hint should be not updated to the new contig. This commit mainly fixes this invariant breakage and includes more: - Handle the cases where the new contig overlaps with the contig_hint or with scan_hint. - Merge the new contig with other hints when it overlaps with them and treat it as a whole free region instead of a separate small region. - Fix the invariant breakage and also optimizes scan_hint further. Some of the optimization cases when no overlap occurs are: - if (new contig > contig_hint > scan_hint) && (scan_hint_start < new contig start < contig_hint_start), then keep scan_hint instead of invalidating it. - if (new contig > contig_hint == scan_hint) && (contig_hint_start < new contig start < scan_hint_start), then update scan_hint to the old contig_hint instead of invalidating it. - if (new contig == contig_hint > scan_hint) && (new contig start < contig_hint_start) && the new contig is to become a new contig_hint due to its better alignment, then update scan_hint to the old contig_hint instead of invalidating or keeping it. Link: https://lore.kernel.org/20260510072149.1279887-4-joonwonkang@google.com Signed-off-by: Joonwon Kang Cc: Christoph Lameter Cc: Dennis Zhou Cc: Tejun Heo Cc: Signed-off-by: Andrew Morton --- mm/percpu.c | 119 +++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 94 insertions(+), 25 deletions(-) --- a/mm/percpu.c~percpu-fix-hint-invariant-breakage +++ a/mm/percpu.c @@ -616,6 +616,20 @@ static inline bool pcpu_region_overlap(s return (a.start < b.start + b.size) && (b.start < a.start + a.size); } +/* + * pcpu_region_concat - determines if two regions meet on the border + * @a: first region + * @b: second region + * + * This is used to determine if the hint region [a.start, a.start + a.size) + * meets with the allocated region [b.start, b.start + b.size) on the border. + */ +static inline bool pcpu_region_concat(struct pcpu_region a, + struct pcpu_region b) +{ + return (a.start == b.start + b.size) || (b.start == a.start + a.size); +} + /** * pcpu_block_update - updates a block given a free area * @block: block of interest @@ -629,6 +643,40 @@ static inline bool pcpu_region_overlap(s static void pcpu_block_update(struct pcpu_block_md *block, int start, int end) { struct pcpu_region free = { .start = start, .size = end - start }; + bool overlap_with_contig_hint = + block->contig_hint.size && + (pcpu_region_overlap(block->contig_hint, free) || + pcpu_region_concat(block->contig_hint, free)); + + if (block->scan_hint.size && + (pcpu_region_overlap(block->scan_hint, free) || + pcpu_region_concat(block->scan_hint, free))) { + start = min(start, block->scan_hint.start); + end = max(end, block->scan_hint.start + block->scan_hint.size); + free = (struct pcpu_region){ + .start = start, + .size = end - start, + }; + + block->scan_hint.size = 0; + } + + if (overlap_with_contig_hint) { + start = min(start, block->contig_hint.start); + end = max(end, + block->contig_hint.start + block->contig_hint.size); + free = (struct pcpu_region){ + .start = start, + .size = end - start, + }; + + if (block->scan_hint.size && + free.size > block->scan_hint.size && + block->scan_hint.start > free.start) + block->scan_hint.size = 0; + + block->contig_hint = free; + } block->first_free = min(block->first_free, free.start); if (free.start == 0) @@ -637,23 +685,24 @@ static void pcpu_block_update(struct pcp if (free.start + free.size == block->nr_bits) block->right_free = free.size; + if (overlap_with_contig_hint) + return; + + /* + * At this point, it is guaranteed that the new contig does neither + * overlap with contig_hint nor with scan_hint. + */ + if (free.size > block->contig_hint.size) { /* promote the old contig_hint to be the new scan_hint */ if (block->contig_hint.size && free.start > block->contig_hint.start) { - if (block->contig_hint.size > block->scan_hint.size) { + if (block->contig_hint.size > block->scan_hint.size || + free.start < block->scan_hint.start) block->scan_hint = block->contig_hint; - } else if (block->scan_hint.size && - free.start < block->scan_hint.start) { - /* - * The old contig_hint.size == scan_hint.size. - * But, the new contig is larger so hold the - * invariant scan_hint.start < - * contig_hint.start. - */ - block->scan_hint.size = 0; - } - } else { + } else if (!block->contig_hint.size || + (block->scan_hint.size && + free.start < block->scan_hint.start)) { block->scan_hint.size = 0; } block->contig_hint = free; @@ -661,21 +710,41 @@ static void pcpu_block_update(struct pcp if (block->contig_hint.start && (!free.start || __ffs(free.start) > __ffs(block->contig_hint.start))) { + if (block->contig_hint.size > block->scan_hint.size) { + if (free.start < block->contig_hint.start) + block->scan_hint = block->contig_hint; + } else if (free.start > block->scan_hint.start) { + /* + * old contig_hint.size == old scan_hint.size + * == new contig size. But, the new contig is + * farther than the old scan_hint so hold the + * invariant scan_hint.start > contig_hint.start + * iff scan_hint.size == contig_hint.size. + */ + block->scan_hint.size = 0; + } + /* new start has a better alignment so use it */ block->contig_hint.start = free.start; - if (block->scan_hint.size && - free.start < block->scan_hint.start && - block->contig_hint.size > block->scan_hint.size) - block->scan_hint.size = 0; - } else if ((block->scan_hint.size && - free.start > block->scan_hint.start) || - block->contig_hint.size > block->scan_hint.size) { - /* - * Knowing new contig size == contig_hint.size, update - * the scan_hint if it is farther than or larger than - * the current scan_hint. - */ - block->scan_hint = free; + } else { + if (block->contig_hint.size > block->scan_hint.size) { + if (free.start < block->contig_hint.start) { + /* + * old scan_hint.size < new contig size + * == old contig_hint.size. But, the new + * contig is before the old contig_hint + * so hold the invariant + * scan_hint.start > contig_hint.start + * iff scan_hint.size == + * contig_hint.size. + */ + block->scan_hint.size = 0; + } else { + block->scan_hint = free; + } + } else if (free.start > block->scan_hint.start) { + block->scan_hint = free; + } } } else { /* _ Patches currently in -mm which might be from joonwonkang@google.com are a.patch