From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id EE8496A013; Wed, 14 Feb 2024 16:25:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707927914; cv=none; b=iLdAsyJ1LmlfSM9LsBVw/OuRaOkrW+DuBE/hs5gpU1K37+xd5V3SNclI9o84bCSgHOnIExOIp1TaCq4zaKFX6eO/em1DnHMiRw65x76vRehwjwC7pBiHlLmWqUM+LTCg01k2+p0ovlqn7jDAX2ra9Ivu8FnLIUsn7aF64pDSZNE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707927914; c=relaxed/simple; bh=Iz4EgZOSFR1zigQnY5oEHTIwS7VOPzZ8Ty+S62gU0GM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HSp3LTGlL9/0OBaMaOgeXSM2e6lLzO37ktcoxVoCHqyutk07E6wayDHgowDOIkRAPuZq0Q0akK7YR6syHtT1QhE4l5+Ci2A5PHqZVPrzTyn+ckbwdPekKA8q3sZoL0ugixZGJnmVqE/D5JwVHrQ+jUpkc6AjIvVR3wy/0eX65AY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4018E1FB; Wed, 14 Feb 2024 08:25:52 -0800 (PST) Received: from [10.57.64.120] (unknown [10.57.64.120]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AFAD03F762; Wed, 14 Feb 2024 08:25:08 -0800 (PST) Message-ID: <48e15a5a-b8e8-4ed7-91df-049f5525f648@arm.com> Date: Wed, 14 Feb 2024 16:25:07 +0000 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 6/7] mm: truncate: split huge page cache page to a non-zero order if possible. Content-Language: en-GB To: Zi Yan Cc: "Pankaj Raghav (Samsung)" , linux-mm@kvack.org, "Matthew Wilcox (Oracle)" , David Hildenbrand , Yang Shi , Yu Zhao , "Kirill A . Shutemov" , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Roman Gushchin , Zach O'Keefe , Hugh Dickins , Mcgrof Chamberlain , Andrew Morton , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20240213215520.1048625-1-zi.yan@sent.com> <20240213215520.1048625-7-zi.yan@sent.com> <1C274CBB-C809-442E-9575-858460C0F62D@nvidia.com> From: Ryan Roberts In-Reply-To: <1C274CBB-C809-442E-9575-858460C0F62D@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 14/02/2024 16:19, Zi Yan wrote: > On 14 Feb 2024, at 5:43, Ryan Roberts wrote: > >> On 13/02/2024 21:55, Zi Yan wrote: >>> From: Zi Yan >>> >>> To minimize the number of pages after a huge page truncation, we do not >>> need to split it all the way down to order-0. The huge page has at most >>> three parts, the part before offset, the part to be truncated, the part >>> remaining at the end. Find the greatest common divisor of them to >>> calculate the new page order from it, so we can split the huge >>> page to this order and keep the remaining pages as large and as few as >>> possible. >>> >>> Signed-off-by: Zi Yan >>> --- >>> mm/truncate.c | 21 +++++++++++++++++++-- >>> 1 file changed, 19 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/truncate.c b/mm/truncate.c >>> index 725b150e47ac..49ddbbf7a617 100644 >>> --- a/mm/truncate.c >>> +++ b/mm/truncate.c >>> @@ -21,6 +21,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include "internal.h" >>> >>> /* >>> @@ -210,7 +211,8 @@ int truncate_inode_folio(struct address_space *mapping, struct folio *folio) >>> bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) >>> { >>> loff_t pos = folio_pos(folio); >>> - unsigned int offset, length; >>> + unsigned int offset, length, remaining; >>> + unsigned int new_order = folio_order(folio); >>> >>> if (pos < start) >>> offset = start - pos; >>> @@ -221,6 +223,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) >>> length = length - offset; >>> else >>> length = end + 1 - pos - offset; >>> + remaining = folio_size(folio) - offset - length; >>> >>> folio_wait_writeback(folio); >>> if (length == folio_size(folio)) { >>> @@ -235,11 +238,25 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) >>> */ >>> folio_zero_range(folio, offset, length); >>> >>> + /* >>> + * Use the greatest common divisor of offset, length, and remaining >>> + * as the smallest page size and compute the new order from it. So we >>> + * can truncate a subpage as large as possible. Round up gcd to >>> + * PAGE_SIZE, otherwise ilog2 can give -1 when gcd/PAGE_SIZE is 0. >>> + */ >>> + new_order = ilog2(round_up(gcd(gcd(offset, length), remaining), >>> + PAGE_SIZE) / PAGE_SIZE); >> >> Given you have up to 2 regions remaining, isn't it possible that you want a >> different order for both those regions (or even multiple orders within the same >> region)? I guess you just choose gcd for simplicity? > > Right. You raise the same concern as Hugh[1]. I am minimizing the call of > split_huge_page_to_list_to_order() and you and Hugh want to minimize the > number of folios after the split. Yours will give better outcome after split, > but requires either multiple calls or a more sophisticated implementation > of page split[2]. We probably can revisit this once splitting to any order > gets wider use. Yeah, fair enough. Sorry hadn't read Hugh's original feedback. > >>> + >>> + /* order-1 THP not supported, downgrade to order-0 */ >>> + if (new_order == 1) >>> + new_order = 0; >> >> I guess this would need to change if supporting order-1 file folios? > > Right. > >>> + >>> + >>> if (folio_has_private(folio)) >>> folio_invalidate(folio, offset, length); >>> if (!folio_test_large(folio)) >>> return true; >>> - if (split_folio(folio) == 0) >>> + if (split_huge_page_to_list_to_order(&folio->page, NULL, new_order) == 0) >> >> I know you are discussing removing this patch, but since you created >> split_folio_to_order() wouldn't that be better here? > > Sure. Will change the patch locally. > > [1] https://lore.kernel.org/linux-mm/9dd96da-efa2-5123-20d4-4992136ef3ad@google.com/ > [2] https://lore.kernel.org/linux-mm/0AC0520E-1BD2-497E-A7ED-05394400BFC9@nvidia.com/ > > -- > Best Regards, > Yan, Zi