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 3EBE922E3F0; Sat, 1 Aug 2026 09:36:21 +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=1785576983; cv=none; b=Wn6QW0so0akl81rcCVH5LSm6E4ghE0HhRYKG2NGgEMAgd86OafglRsGurYCtt2DF0TwdDEvt/Ye+vYTJfMHQvKDnVRm4YBHksXh+kwQebMpXFY7TzFJgLfHDqF1Am2Qf3hoRsQw4MMLLBx5wos3H7n8/OJrIEaw46r57eEqATCw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785576983; c=relaxed/simple; bh=CEe/FRprcKODc2y9BNtL9FlextKV3tyXyPlJXZJA/Vk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ecvS4kThZ0ff8vE+Xg7giijwnetkX8KYqIJHp5L2ed5a/pQm49nW4Q4vRKnVkPnm9YewDzrFXtu/NNgOVjnbRRLHJYy1MyAqkEC/1raaFFnZC4TtNlvBQddISuoC0wl8yFqr+qMrcEjPeRhPvrb0gajOdv/DLTXSwUtNMa4cY1A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mZaAr1pW; 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="mZaAr1pW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 154941F00AC4; Sat, 1 Aug 2026 09:36:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785576981; bh=709PrRE4T6mqHxV2NldJPDtfXEbe8pwqFIDr7kni5hQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=mZaAr1pWTIuDLBtCszvPR8u1+iDcJ95gaenhrfArddi5Uu4gBhXOIyw/4zH7JfxXI 5l2zs5HbYWmIj6FsSB00mOpWBEvqjRrOmyozQlsFES9VE3iwdUSkINUJKb/0E5iHC9 dkT/beAsMUAHwXIYHraJ/X8arV7DA2dxu/t+94Ds5t23AN9ys2S1+g6wc96k3RKRf2 3qMIAMLEyZ+6d+hMmPIRtHkaB70dB18NWQBxjcyzRzMo2dcBoxiiGR8zd/xfxGqw22 Eb/w8ugVZkU5p18je3Sc34gGWTAqVH6v/nWLiwUvTFeTDFZYN18droYQ6KA/dE8+E6 zn6/ma2FuClxw== Date: Sat, 1 Aug 2026 10:36:03 +0100 From: "Lorenzo Stoakes (ARM)" To: Zi Yan Cc: Johannes Weiner , Andrew Morton , Matthew Wilcox , William Kucharski , David Hildenbrand , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 1/2] mm/huge_memory: use folio's memcg inside __folio_split() Message-ID: References: <20260730-add-gfp_account-to-xas_split_alloc-v2-0-5a56c2361d85@nvidia.com> <20260730-add-gfp_account-to-xas_split_alloc-v2-1-5a56c2361d85@nvidia.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260730-add-gfp_account-to-xas_split_alloc-v2-1-5a56c2361d85@nvidia.com> On Thu, Jul 30, 2026 at 10:18:00PM -0400, Zi Yan wrote: > During a pagecache folio split, an xarray node allocation can happen and > needs to charge at folio's memcg instead of folio split invoker's memcg, > because for example folio split can happen during reclaim and reclaim's > active memcg might not be folio's memcg. Switch to folio's memcg at the > beginning and switch back afterwards. I assume this is the only allocation? I guess in general it makes sense to have the folio's memcg be active here regardless. > > Suggested-by: Johannes Weiner > Fixes: 6b24ca4a1a8d4 ("mm: Use multi-index entries in the page cache") Cc: stable? > Signed-off-by: Zi Yan Change seems reasonable overall. Acked-by: Lorenzo Stoakes (ARM) > --- > mm/huge_memory.c | 20 ++++++++++++++++---- > 1 file changed, 16 insertions(+), 4 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 04e8a6b553435..b9c2d8908e564 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -4063,34 +4063,42 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > XA_STATE(xas, &folio->mapping->i_pages, folio->index); > struct folio *end_folio = folio_next(folio); > bool is_anon = folio_test_anon(folio); > + struct mem_cgroup *memcg, *old_memcg; > struct address_space *mapping = NULL; > struct anon_vma *anon_vma = NULL; > int old_order = folio_order(folio); > struct folio *new_folio, *next; > int nr_shmem_dropped = 0; > enum ttu_flags ttu_flags = 0; > - int ret; > pgoff_t end = 0; > + int ret; > > VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); > VM_WARN_ON_ONCE_FOLIO(!folio_test_large(folio), folio); > > if (folio != page_folio(split_at) || folio != page_folio(lock_at)) { > ret = -EINVAL; > - goto out; > + goto out_no_memcg; > } > > if (new_order >= old_order) { > ret = -EINVAL; > - goto out; > + goto out_no_memcg; > } > > ret = folio_check_splittable(folio, new_order, split_type); > if (ret) { > VM_WARN_ONCE(ret == -EINVAL, "Tried to split an unsplittable folio"); > - goto out; > + goto out_no_memcg; This function really badly needs splitting up and probably some cleanup.h work :) > } > > + /* > + * switch to folio's memcg as xarray node allocation can happen and > + * needs to charge to it. > + */ > + memcg = get_mem_cgroup_from_folio(folio); > + old_memcg = set_active_memcg(memcg); > + > if (is_anon) { > /* > * The caller does not necessarily hold an mmap_lock that would > @@ -4231,6 +4239,10 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > if (mapping) > i_mmap_unlock_read(mapping); > out: > + /* restore to caller's old_memcg */ > + set_active_memcg(old_memcg); > + mem_cgroup_put(memcg); > +out_no_memcg: > xas_destroy(&xas); > if (is_pmd_order(old_order)) > count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED); > > -- > 2.53.0 > -- Cheers, Lorenzo