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 4F051353A66 for ; Mon, 3 Aug 2026 08:03:36 +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=1785744218; cv=none; b=VBmwsS6ithPKUjSRNaKKDY1efEoKeW0RiZdZJTi2zwTmsujPMfBbS5dSdWlTku/knP5ypxZqutj0l56p5N7h0Lz5oNze1lM+OlF1cbOI1rs9+vToYkBRikJqRPk52Grb88AFVHqqcM+fViIPED77VFb4RzktlTRe2o3mg73K9D4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785744218; c=relaxed/simple; bh=ZSzHvVViXfxJVabHBt2iIKBPY2mp2ly2KLZb0yBU5OE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=C8mcr3YlsgEa8TznVHRJDn8y7gyuuHkFf4aoMcyqEaMM/ycg8lSLweqlr959CzanhRqHJhMrcav8/zZVT50jXmTzCaa9QnlbxmKtxBR+nmvC9atsjbDDIDHqgKlmrqZjGuZC85MMvV86OlUb5Er0baWewygbN5gIwnIYJmDY0C8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VKt0ev36; 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="VKt0ev36" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 94DFE1F000E9; Mon, 3 Aug 2026 08:03:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785744216; bh=UzQBOSdM8d5X4KazmRx/5dOzwR4xvWcih6CFGjod+k4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=VKt0ev36BT3N/oyYml6Oz7KOswtKD+GwJbS+MB6y6jrMJ+wF3KAt7UZyAlbvo1C5M 7tFIFsyU+ADcWjdUgj3L9M7uFyh9P2nUrSSCXBvfzr1lU0MjRGZQuz1z3pz9XfjZC8 64EZuAA4GSX8Rwxv9uX/xRUeBK+FWkq2Q1s/IZmWD40+Lij6oih+mKsYRQn3xutP0b 0XO99QYvfgazYuG5GRS6S7fcEuINPkHSMLd4FHfTDUgzSjDO96na35fVJjfiEP6KXw IK0NBNoyw6Iku/4PH7vVdJQ/0HpOqFGNNT2HlVX72JugeJB1MtSHw/8clpznUWsM40 rNFOrhXuHB/Hw== Message-ID: Date: Mon, 3 Aug 2026 10:03:29 +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: [RFC PATCH v2 2/2] mm: improve large folio reuse for LRU-cached folios To: Barry Song Cc: akpm@linux-foundation.org, linux-mm@kvack.org, ljs@kernel.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, lance.yang@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, npache@redhat.com, ryan.roberts@arm.com, ziy@nvidia.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com References: <20260709081536.82768-1-baohua@kernel.org> <20260709081536.82768-3-baohua@kernel.org> <8f74bd51-11f2-4837-9463-d016444e45cc@kernel.org> 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 8/3/26 09:24, Barry Song wrote: > On Wed, Jul 29, 2026 at 8:11 PM David Hildenbrand (Arm) > wrote: >> >> On 7/9/26 10:15, Barry Song (Xiaomi) wrote: >>> Large folios may now reside in the per-CPU LRU cache. Before >>> attempting to reuse them, drain the local LRU cache, which >>> can still be beneficial in cases where the folios are likely >>> to remain in this CPU's LRU cache: >>> >>> int main(int argc, char *argv[]) >>> { >>> int i; >>> while (1) { >>> volatile int *p = mmap(0, SIZE, PROT_READ | PROT_WRITE, >>> MAP_PRIVATE | MAP_ANONYMOUS, >>> -1, 0); >>> for (int i = 0; i < SIZE / sizeof(int); i++) >>> p[i] = i; >>> madvise((void *)p, SIZE, MADV_PAGEOUT); >>> if (!fork()) >>> _exit(0); >>> for (int i = 0; i < SIZE / sizeof(int); i++) >>> p[i] = i; >>> munmap((void *)p, SIZE); >>> } >>> return 0; >>> } >>> >>> Signed-off-by: Barry Song (Xiaomi) >>> --- >>> mm/memory.c | 13 +++++++++++++ >>> 1 file changed, 13 insertions(+) >>> >>> diff --git a/mm/memory.c b/mm/memory.c >>> index 5689b7cff76c..1d08ed5ba99b 100644 >>> --- a/mm/memory.c >>> +++ b/mm/memory.c >>> @@ -4136,6 +4136,19 @@ static bool __wp_can_reuse_large_anon_folio(struct folio *folio, >>> folio_unlock(folio); >>> } >>> >>> + if (folio_may_be_lru_cached(folio) && !folio_test_lru(folio)) { >>> + if (folio_ref_count(folio) > folio_large_mapcount(folio) + 1) >> >> I assume that can just be a "!=". > > I was trying to guard against the case where a folio is not on > the LRU but also does not hold an extra reference. For example, > the folio is off the LRU, yet > folio_ref_count(folio) == folio_large_mapcount(folio). > > In that case, we could simply reuse !folio_test_lru(folio). > > Maybe such a case cannot actually happen, since paths like > isolate_folio() take an extra reference before removing the > folio from the LRU. > > So we should be ok to just use folio_ref_count(folio) != > folio_large_mapcount(folio) +1 I just stumbled into something nasty last week: https://lore.kernel.org/r/20260731-check_and_migrate_movable_folios-v1-1-e0002d7b791e@kernel.org For an mTHP, if we end up pinning multiple pages, calculating pin_refs is problematic and might require us to batch over multiple pages. But there are some nasty corner cases when just batching contiguous pages. -- Cheers, David