From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 41A693603EF for ; Wed, 26 Aug 2026 07:23:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787729025; cv=none; b=tBS29ZPBGjX/Q70xr2xLywh1xCnbuXCvVZkbLcnXQmgrmf/o7QqwciNo1dhr5dA3J+Av2435sIPlc3sFzsfh4btPk0a1sudVe5MR6J4GnKuxDpKOFaHDc2zfvzeQhpyS/6v1fPV/uFFzaUqcNqYayw3c1jHYs8LuKTeVF8cCzdA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787729025; c=relaxed/simple; bh=xxq4sLyGOO6aXCeijfTHnVX+3p/AQ96PSQ6dcIRP1iY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Ugstv6nca0Glepx0BBJTQjrTDAy5kqpkbfzvSX57vp2sYdDy6JQ+tRcPe/Hfwu4/7g5UgMw9gH7IFKYOmzOilWSVokgraU9zBlOxJ1+D35MvelQgPOxv0Os4rzPHmWDz0mxqEDYd/BOx17NWQkzp/nQTPdudZOKU4fr8J3uNZIY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bk9h0TQk; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bk9h0TQk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 28F671F000E9; Wed, 26 Aug 2026 07:23:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787729021; bh=eDY+D7XL9VuOmqDyV1cbNPo/RBpqAzB2FjfOhAjGhW8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=bk9h0TQkoAsdrTAfvO7bJZAqgBEtCuTbokVkteESGBqJymGQQiW+EDuaRW/do3qr9 K/bjqs93XO0Vt3LolPNeKkksBx21/D2yiDHbPORUOWE85JfnQYIzhSH1Rv7oaNRdqj xFYfrNZzdEssI1zf34ftP8+LhtM7MDlFvUsO6NW7mSgM+fQSbZfvdM2HUM7DJAIpMM N+hUg3SevjHZoIbLmNrvZukDUrKCQ+i8t8tkKb1vTGzJSX84HduHP3mzdapPFzTHmf +iFP0L8XS2gMb4plOera5hojjcBidjkuKhKFnMZjZ9u/bW5CCCCxwZyyzaFKji4wdi tQrDlCBYgNhvg== Message-ID: <24f8108d-e7e7-47d6-8994-f50625daa4f0@kernel.org> Date: Wed, 26 Aug 2026 09:23:37 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/hugetlb: fix missing migratable flag on same-node hugetlb migration To: mawupeng , muchun.song@linux.dev, osalvador@suse.de, akpm@linux-foundation.org, baolin.wang@linux.alibaba.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260707110254.3147686-1-mawupeng1@huawei.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/26/26 03:46, mawupeng wrote: > > > On 周二 2026-8-25 18:27, David Hildenbrand (Arm) wrote: >> On 7/7/26 13:02, Wupeng Ma wrote: >>> Commit ba23f58de896 ("mm/migrate: don't call >>> folio_putback_active_hugetlb() on dst hugetlb folio") moved setting of >>> the migratable flag and active-list placement from >>> folio_putback_active_hugetlb(dst) into move_hugetlb_state(), so that >>> the freshly allocated destination folio is handled where allocation is >>> known to have succeeded. >>> >>> Unfortunately, the new code was appended after the existing >>> temporary-folio block in move_hugetlb_state(), which contains an early >>> return added earlier by commit 5af1ab1d24e08 ("mm/hugetlb: optimize >>> the surplus state transfer code in move_hugetlb_state()"): >>> >>> if (folio_test_hugetlb_temporary(new_folio)) { >>> ... >>> if (new_nid == old_nid) >>> return; <-- skips the new code >>> ... >>> } >>> >>> /* added by ba23f58 */ >>> folio_set_hugetlb_migratable(new_folio); >>> list_move_tail(&new_folio->lru, ...&h->hugepage_activelist); >>> >>> When the destination folio is temporary (i.e. the hugetlb pool was >>> exhausted and the migration callback fell back to >>> alloc_migrate_hugetlb_folio()) and the migration does not cross a >>> node -- the common case, and always true on a single-NUMA system -- >>> move_hugetlb_state() returns before setting the migratable flag or >>> adding the new folio to the active list. The destination folio is >>> then installed in the page table but cannot be isolated afterwards, >>> since folio_isolate_hugetlb() rejects folios without the migratable >>> flag; a subsequent soft-offline, hard-offline or memory-hotplug >>> offline of that folio fails with -EBUSY. >>> >>> This was reproduced on a single-NUMA arm64 VM: a second >>> MADV_SOFT_OFFLINE on an already-migrated hugetlb page returned EBUSY >>> and logged "hugepage isolation failed". >>> >>> Keep the surplus adjustment, which is the only part that depends on >>> the node crossing, guarded by `if (new_nid != old_nid)', while making >>> the migratable flag and active-list placement unconditional. This >>> preserves the cleanup intent of ba23f58 and closes the early-return >>> hole. >>> >>> Fixes: ba23f58de896 ("mm/migrate: don't call folio_putback_active_hugetlb() on dst hugetlb folio") >> >> Agreed, let's CC stable. > > Thanks. > >> >>> Signed-off-by: Wupeng Ma >>> --- >>> mm/hugetlb.c | 14 +++++++------- >>> 1 file changed, 7 insertions(+), 7 deletions(-) >>> >>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>> index 571212b80835..cafadfdb63c0 100644 >>> --- a/mm/hugetlb.c >>> +++ b/mm/hugetlb.c >>> @@ -7211,14 +7211,14 @@ void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio, int re >>> * There is no need to transfer the per-node surplus state >>> * when we do not cross the node. >>> */ >>> - if (new_nid == old_nid) >>> - return; >>> - spin_lock_irq(&hugetlb_lock); >>> - if (h->surplus_huge_pages_node[old_nid]) { >>> - h->surplus_huge_pages_node[old_nid]--; >>> - h->surplus_huge_pages_node[new_nid]++; >>> + if (new_nid != old_nid) { >>> + spin_lock_irq(&hugetlb_lock); >>> + if (h->surplus_huge_pages_node[old_nid]) { >>> + h->surplus_huge_pages_node[old_nid]--; >>> + h->surplus_huge_pages_node[new_nid]++; >>> + } >>> + spin_unlock_irq(&hugetlb_lock); >>> } >> >> The return was really rather hidden, thanks! >> >> Can't we instead just turn the "return;" into a "continue;" ? > > There’s no loop in move_hugetlb_state(), so continue won’t work there. But I understand your intention. I am clearly in need of some vacation (next week!!! :) ). > To be honest, I’m not fully satisfied with the nested if either, but I haven’t found a cleaner way. > goto, or extracting the surplus move into a helper, feels like over-engineering. Nah, let's keep it like it is, thanks! Acked-by: David Hildenbrand (Arm) -- Cheers, David