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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Yu Zhao <yuzhao@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Andi Kleen <ak@linux.intel.com>,
	Aneesh Kumar <aneesh.kumar@linux.ibm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Hillf Danton <hdanton@sina.com>, Jens Axboe <axboe@kernel.dk>,
	Jesse Barnes <jsbarnes@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Matthew Wilcox <willy@infradead.org>,
	Mel Gorman <mgorman@suse.de>,
	Michael Larabel <Michael@michaellarabel.com>,
	Michal Hocko <mhocko@kernel.org>, Mike Rapoport <rppt@kernel.org>,
	Rik van Riel <riel@surriel.com>, Vlastimil Babka <vbabka@suse.cz>,
	Will Deacon <will@kernel.org>, Ying Huang <ying.huang@intel.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	Kernel Page Reclaim v2 <page-reclaim@google.com>,
	"the arch/x86 maintainers" <x86@kernel.org>
Subject: Re: [PATCH v8 00/14] Multi-Gen LRU Framework
Date: Tue, 8 Mar 2022 16:29:33 -0800	[thread overview]
Message-ID: <CAHk-=wgwgqJMyxbrxa-mY3cYh--BZ5JKDieVc=RfXR1mdqsYkQ@mail.gmail.com> (raw)
In-Reply-To: <CAOUHufYFDawK6vmkQ16EQm7FSHresViifnxW2yj_RDuMSjJPjg@mail.gmail.com>

On Tue, Mar 8, 2022 at 4:15 PM Yu Zhao <yuzhao@google.com> wrote:
>
> This sounds self-serving: our data centers want them, so I had to try.

Heh. I'm not opposed to putting them back in, but if/when we merge the
multi-gen LRU code, I really want people to be all testing the same
thing.

I also think that if we put them back in, that should come with

 (a) performance numbers for the different cases

 (b) hard guidance of what the numbers should be, and under what
circumstances (ie giving the user enough information that he *can*
answer the question for his configuration)

 (c) some thought about perhaps making them possibly more dynamic than
a hardcoded build-time value (assuming the numbers show that it's
worth doing in the first place, of course)

so I think that the support for the concept can/should be left in, but
I think that kind of fancy "I want more generations or fewer
tiers-per-generation because of XYZ" needs to be a separate issue with
more explanation from the initial "This multi-gen LRU gives better
performance" merge.

Because as-is, I don't think those config options had nearly enough
information associated with them to merit them existing.

                  Linus

WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Yu Zhao <yuzhao@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Andi Kleen <ak@linux.intel.com>,
	Aneesh Kumar <aneesh.kumar@linux.ibm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	 Dave Hansen <dave.hansen@linux.intel.com>,
	Hillf Danton <hdanton@sina.com>,  Jens Axboe <axboe@kernel.dk>,
	Jesse Barnes <jsbarnes@google.com>,
	 Johannes Weiner <hannes@cmpxchg.org>,
	Jonathan Corbet <corbet@lwn.net>,
	 Matthew Wilcox <willy@infradead.org>,
	Mel Gorman <mgorman@suse.de>,
	 Michael Larabel <Michael@michaellarabel.com>,
	Michal Hocko <mhocko@kernel.org>, Mike Rapoport <rppt@kernel.org>,
	Rik van Riel <riel@surriel.com>, Vlastimil Babka <vbabka@suse.cz>,
	 Will Deacon <will@kernel.org>, Ying Huang <ying.huang@intel.com>,
	 Linux ARM <linux-arm-kernel@lists.infradead.org>,
	 "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	 Kernel Page Reclaim v2 <page-reclaim@google.com>,
	"the arch/x86 maintainers" <x86@kernel.org>
Subject: Re: [PATCH v8 00/14] Multi-Gen LRU Framework
Date: Tue, 8 Mar 2022 16:29:33 -0800	[thread overview]
Message-ID: <CAHk-=wgwgqJMyxbrxa-mY3cYh--BZ5JKDieVc=RfXR1mdqsYkQ@mail.gmail.com> (raw)
In-Reply-To: <CAOUHufYFDawK6vmkQ16EQm7FSHresViifnxW2yj_RDuMSjJPjg@mail.gmail.com>

On Tue, Mar 8, 2022 at 4:15 PM Yu Zhao <yuzhao@google.com> wrote:
>
> This sounds self-serving: our data centers want them, so I had to try.

Heh. I'm not opposed to putting them back in, but if/when we merge the
multi-gen LRU code, I really want people to be all testing the same
thing.

I also think that if we put them back in, that should come with

 (a) performance numbers for the different cases

 (b) hard guidance of what the numbers should be, and under what
circumstances (ie giving the user enough information that he *can*
answer the question for his configuration)

 (c) some thought about perhaps making them possibly more dynamic than
a hardcoded build-time value (assuming the numbers show that it's
worth doing in the first place, of course)

so I think that the support for the concept can/should be left in, but
I think that kind of fancy "I want more generations or fewer
tiers-per-generation because of XYZ" needs to be a separate issue with
more explanation from the initial "This multi-gen LRU gives better
performance" merge.

Because as-is, I don't think those config options had nearly enough
information associated with them to merit them existing.

                  Linus

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2022-03-09  1:13 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-08 23:47 [PATCH v8 00/14] Multi-Gen LRU Framework Yu Zhao
2022-03-08 23:47 ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 01/14] mm: x86, arm64: add arch_has_hw_pte_young() Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 02/14] mm: x86: add CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 03/14] mm/vmscan.c: refactor shrink_node() Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 04/14] Revert "include/linux/mm_inline.h: fold __update_lru_size() into its sole caller" Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 05/14] mm: multi-gen LRU: groundwork Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:58   ` Linus Torvalds
2022-03-08 23:58     ` Linus Torvalds
2022-03-08 23:47 ` [PATCH v8 06/14] mm: multi-gen LRU: minimal implementation Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-09  0:02   ` Linus Torvalds
2022-03-09  0:02     ` Linus Torvalds
2022-03-08 23:47 ` [PATCH v8 07/14] mm: multi-gen LRU: exploit locality in rmap Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 08/14] mm: multi-gen LRU: support page table walks Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 09/14] mm: multi-gen LRU: optimize multiple memcgs Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 10/14] mm: multi-gen LRU: kill switch Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 11/14] mm: multi-gen LRU: thrashing prevention Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 12/14] mm: multi-gen LRU: debugfs interface Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 13/14] mm: multi-gen LRU: admin guide Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-08 23:47 ` [PATCH v8 14/14] mm: multi-gen LRU: design doc Yu Zhao
2022-03-08 23:47   ` Yu Zhao
2022-03-09  0:06 ` [PATCH v8 00/14] Multi-Gen LRU Framework Linus Torvalds
2022-03-09  0:06   ` Linus Torvalds
2022-03-09  0:14   ` Yu Zhao
2022-03-09  0:14     ` Yu Zhao
2022-03-09  0:29     ` Linus Torvalds [this message]
2022-03-09  0:29       ` Linus Torvalds

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