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 778CB18C908 for ; Fri, 9 Aug 2024 07:50:04 +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=1723189806; cv=none; b=o7kUMl6dlQTo3FMpoppTxw6d48lhezDLEECK6cfQIkCu0eYC3bzCYHX740TDBpitnQzgo8aSwOyUjuYW2KszCWgLgTfm8HHRtezeyBIBbeh6x/Oe9ABiBSRhErD4bMasE/bvJZBkqAVOlay0iro/VoNyrjst1Qvl8wz+4aY4+Ts= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723189806; c=relaxed/simple; bh=wvowNK+xjpvrALPymf1A/xsuwNtpEMJYLAEFACXuZ6o=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YUxZ7TP52qAFileY+3Iv/m/Ia3uu4bQI/GLCi2EmaUARhbFTsix2662//EAEoktYa3HXJeKBx+E49erfTTIEI/7kT0K9ofwPuLZTBlYMQOPWHqtINYZw543otlGYH1Mpc/REsywSmYu1cGNzSUpVoMHDCYetZLEMKILmPgxQZQY= 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 79DCDFEC; Fri, 9 Aug 2024 00:50:29 -0700 (PDT) Received: from [10.57.95.64] (unknown [10.57.95.64]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7E46B3F6A8; Fri, 9 Aug 2024 00:50:02 -0700 (PDT) Message-ID: <41658cce-6cd8-47bf-b9bd-657e0a362d11@arm.com> Date: Fri, 9 Aug 2024 08:50:00 +0100 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 1/2] mm: add per-order mTHP split counters Content-Language: en-GB To: Barry Song Cc: Lance Yang , akpm@linux-foundation.org, david@redhat.com, baolin.wang@linux.alibaba.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240424135148.30422-1-ioworker0@gmail.com> <20240424135148.30422-2-ioworker0@gmail.com> <71fdab06-0442-4c55-811b-b38d3b024c85@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 08/08/2024 22:27, Barry Song wrote: > On Mon, Jul 1, 2024 at 8:16 PM Ryan Roberts wrote: >> >> On 30/06/2024 12:34, Lance Yang wrote: >>> Hi Barry, >>> >>> Thanks for following up! >>> >>> On Sun, Jun 30, 2024 at 5:48 PM Barry Song wrote: >>>> >>>> On Thu, Apr 25, 2024 at 3:41 AM Ryan Roberts wrote: >>>>> >>>>> + Barry >>>>> >>>>> On 24/04/2024 14:51, Lance Yang wrote: >>>>>> At present, the split counters in THP statistics no longer include >>>>>> PTE-mapped mTHP. Therefore, this commit introduces per-order mTHP split >>>>>> counters to monitor the frequency of mTHP splits. This will assist >>>>>> developers in better analyzing and optimizing system performance. >>>>>> >>>>>> /sys/kernel/mm/transparent_hugepage/hugepages-/stats >>>>>> split_page >>>>>> split_page_failed >>>>>> deferred_split_page >>>>>> >>>>>> Signed-off-by: Lance Yang >>>>>> --- >>>>>> include/linux/huge_mm.h | 3 +++ >>>>>> mm/huge_memory.c | 14 ++++++++++++-- >>>>>> 2 files changed, 15 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >>>>>> index 56c7ea73090b..7b9c6590e1f7 100644 >>>>>> --- a/include/linux/huge_mm.h >>>>>> +++ b/include/linux/huge_mm.h >>>>>> @@ -272,6 +272,9 @@ enum mthp_stat_item { >>>>>> MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE, >>>>>> MTHP_STAT_ANON_SWPOUT, >>>>>> MTHP_STAT_ANON_SWPOUT_FALLBACK, >>>>>> + MTHP_STAT_SPLIT_PAGE, >>>>>> + MTHP_STAT_SPLIT_PAGE_FAILED, >>>>>> + MTHP_STAT_DEFERRED_SPLIT_PAGE, >>>>>> __MTHP_STAT_COUNT >>>>>> }; >>>>>> >>>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>>>> index 055df5aac7c3..52db888e47a6 100644 >>>>>> --- a/mm/huge_memory.c >>>>>> +++ b/mm/huge_memory.c >>>>>> @@ -557,6 +557,9 @@ DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK); >>>>>> DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE); >>>>>> DEFINE_MTHP_STAT_ATTR(anon_swpout, MTHP_STAT_ANON_SWPOUT); >>>>>> DEFINE_MTHP_STAT_ATTR(anon_swpout_fallback, MTHP_STAT_ANON_SWPOUT_FALLBACK); >>>>>> +DEFINE_MTHP_STAT_ATTR(split_page, MTHP_STAT_SPLIT_PAGE); >>>>>> +DEFINE_MTHP_STAT_ATTR(split_page_failed, MTHP_STAT_SPLIT_PAGE_FAILED); >>>>>> +DEFINE_MTHP_STAT_ATTR(deferred_split_page, MTHP_STAT_DEFERRED_SPLIT_PAGE); >>>>>> >>>>>> static struct attribute *stats_attrs[] = { >>>>>> &anon_fault_alloc_attr.attr, >>>>>> @@ -564,6 +567,9 @@ static struct attribute *stats_attrs[] = { >>>>>> &anon_fault_fallback_charge_attr.attr, >>>>>> &anon_swpout_attr.attr, >>>>>> &anon_swpout_fallback_attr.attr, >>>>>> + &split_page_attr.attr, >>>>>> + &split_page_failed_attr.attr, >>>>>> + &deferred_split_page_attr.attr, >>>>>> NULL, >>>>>> }; >>>>>> >>>>>> @@ -3083,7 +3089,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, >>>>>> XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, new_order); >>>>>> struct anon_vma *anon_vma = NULL; >>>>>> struct address_space *mapping = NULL; >>>>>> - bool is_thp = folio_test_pmd_mappable(folio); >>>>>> + int order = folio_order(folio); >>>>>> int extra_pins, ret; >>>>>> pgoff_t end; >>>>>> bool is_hzp; >>>>>> @@ -3262,8 +3268,10 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, >>>>>> i_mmap_unlock_read(mapping); >>>>>> out: >>>>>> xas_destroy(&xas); >>>>>> - if (is_thp) >>>>>> + if (order >= HPAGE_PMD_ORDER) >>>>>> count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED); >>>>>> + count_mthp_stat(order, !ret ? MTHP_STAT_SPLIT_PAGE : >>>>>> + MTHP_STAT_SPLIT_PAGE_FAILED); >>>>>> return ret; >>>>>> } >>>>>> >>>>>> @@ -3327,6 +3335,8 @@ void deferred_split_folio(struct folio *folio) >>>>>> if (list_empty(&folio->_deferred_list)) { >>>>>> if (folio_test_pmd_mappable(folio)) >>>>>> count_vm_event(THP_DEFERRED_SPLIT_PAGE); >>>>>> + count_mthp_stat(folio_order(folio), >>>>>> + MTHP_STAT_DEFERRED_SPLIT_PAGE); >>>>> >>>>> There is a very long conversation with Barry about adding a 'global "mTHP became >>>>> partially mapped 1 or more processes" counter (inc only)', which terminates at >>>>> [1]. There is a lot of discussion about the required semantics around the need >>>>> for partial map to cover alignment and contiguity as well as whether all pages >>>>> are mapped, and to trigger once it becomes partial in at least 1 process. >>>>> >>>>> MTHP_STAT_DEFERRED_SPLIT_PAGE is giving much simpler semantics, but less >>>>> information as a result. Barry, what's your view here? I'm guessing this doesn't >>>>> quite solve what you are looking for? >>>> >>>> This doesn't quite solve what I am looking for but I still think the >>>> patch has its value. >>>> >>>> I'm looking for a solution that can: >>>> >>>> * Count the amount of memory in the system for each mTHP size. >>>> * Determine how much memory for each mTHP size is partially unmapped. >>>> >>>> For example, in a system with 16GB of memory, we might find that we have 3GB >>>> of 64KB mTHP, and within that, 512MB is partially unmapped, potentially wasting >>>> memory at this moment. I'm uncertain whether Lance is interested in >>>> this job :-) >>> >>> Nice, that's an interesting/valuable job for me ;) >>> >>> Let's do it separately, as 'split' and friends probably can’t be the >>> solution you >>> mentioned above, IMHO. >>> >>> Hmm... I don't have a good idea about the solution for now, but will >>> think it over >>> and come back to discuss it here. >> >> I have a grad starting in a couple of weeks and I had been planning to initially >> ask him to look at this to help him get up to speed on mTHP/mm stuff. But I have >> plenty of other things for him to do if Lance wants to take this :) > > Hi Ryan, Lance, > > My performance profiling is pending on the mTHP size and partially > unmapped mTHP size issues (understanding the distribution of folio > sizes within the system), so I'm not waiting for either Ryan's grad > or Lance. I've sent an RFC for this, and both of you are CC'd: > > https://lore.kernel.org/all/20240808010457.228753-1-21cnbao@gmail.com/ Yes I saw that, I'll try to give it some review today. > > Apologies for not waiting. You are still warmly welcomed to participate > in the discussion and review. No problem; after this last discussion, I assumed Lance was going to work on it so there has been no duplicated effort from my side. Glad to see it implemented. > >> >>> >>>> >>>> Counting deferred_split remains valuable as it can signal whether the system is >>>> experiencing significant partial unmapping. >>> >>> Have a nice weekend! >>> Lance >>> >>>> >>>>> >>>>> [1] https://lore.kernel.org/linux-mm/6cc7d781-884f-4d8f-a175-8609732b87eb@arm.com/ >>>>> >>>>> Thanks, >>>>> Ryan >>>>> >>>>>> list_add_tail(&folio->_deferred_list, &ds_queue->split_queue); >>>>>> ds_queue->split_queue_len++; >>>>>> #ifdef CONFIG_MEMCG >>>>> >>>> > > Thanks > Barry