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 8492618E29; Wed, 14 Feb 2024 10:43:47 +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=1707907429; cv=none; b=DUMqhJDJ//r1NSBJrVkAKaUrJ756yw+rPMri2T4e6C1HMIG8pHmzMRaXxD2aZ1aGGnS29ZRAvV8D6Jy17JBfa38Z3jOxPe2UABe+k5VhJEEFd2XcAx8jENQ0fiHrMbn3fVQgPg3rKbEUQK9avMFpjz7TgcjPrB+yEqw2Pe2h4Ys= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707907429; c=relaxed/simple; bh=/d1FtVUVxRZ+e78TMHZblQDSf8Xsk0E7UCHt6C8VlCE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Afrmj1JdWyqVpCkU43GRy89EgeTVQjbUE77EvaPZCSc8+QeMqhQtM91tQDGRLn80Z6zIV+SEgWU9QIMH7PDQDVT0aonLDMYUI33srlxu89HCIF2yPxttWmWADJatda8f9LF1LYeRllkOFcGYTd0OfwM7buFmonRaTew9cXBXhAw= 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 84CA5DA7; Wed, 14 Feb 2024 02:44:27 -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 DE4A83F766; Wed, 14 Feb 2024 02:43:43 -0800 (PST) Message-ID: Date: Wed, 14 Feb 2024 10:43:42 +0000 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 v4 6/7] mm: truncate: split huge page cache page to a non-zero order if possible. Content-Language: en-GB To: Zi Yan , "Pankaj Raghav (Samsung)" , linux-mm@kvack.org Cc: "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> From: Ryan Roberts In-Reply-To: <20240213215520.1048625-7-zi.yan@sent.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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? > + > + /* 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? > + > + > 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? Thanks, Ryan > return true; > if (folio_test_dirty(folio)) > return false;