linux-kernel - Re: [PATCH v1 00/14] Multigenerational LRU

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Date:   Tue, 16 Mar 2021 14:14:43 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     linux-mm@...ck.org, Alex Shi <alex.shi@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Hillf Danton <hdanton@...a.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.com>,
        Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Yang Shi <shy828301@...il.com>,
        Ying Huang <ying.huang@...el.com>,
        linux-kernel@...r.kernel.org, page-reclaim@...gle.com
Subject: Re: [PATCH v1 00/14] Multigenerational LRU

On 3/16/21 1:30 PM, Yu Zhao wrote:
> On Tue, Mar 16, 2021 at 07:50:23AM -0700, Dave Hansen wrote:
>> I think it would also be very worthwhile to include some research in
>> this series about why the kernel moved away from page table scanning.
>> What has changed?  Are the workloads we were concerned about way back
>> then not around any more?  Has faster I/O or larger memory sizes with a
>> stagnating page size changed something?
> 
> Sure. Hugh also suggested this too but I personally found that ancient
> pre-2.4 history too irrelevant (and uninteresting) to the modern age
> and decided to spare audience of the boredom.

IIRC, rmap chains showed up in the 2.5 era and the VM was quite bumpy
until anon_vmas came around, which was early-ish in the 2.6 era.

But, either way, I think there is a sufficient population of nostalgic
crusty old folks around to warrant a bit of a history lesson.  We'll
enjoy the trip down memory lane, fondly remembering the old days in
Ottawa...

>>> nr_vmscan_write 24900719
>>> nr_vmscan_immediate_reclaim 115535
>>> pgscan_kswapd 320831544
>>> pgscan_direct 23396383
>>> pgscan_direct_throttle 0
>>> pgscan_anon 127491077
>>> pgscan_file 216736850
>>> slabs_scanned 400469680
>>> compact_migrate_scanned 1092813949
>>> compact_free_scanned 4919523035
>>> compact_daemon_migrate_scanned 2372223
>>> compact_daemon_free_scanned 20989310
>>> unevictable_pgs_scanned 307388545
> 
> 10G swap + 8G anon rss + 6G file rss, hmm... an interesting workload.
> The file rss does seem a bit high to me, my wild speculation is there
> have been git/make activities in addition to a VM?

I wish I was doing more git/make activities.  It's been an annoying
amount of email and web browsers for 12 days.  If anything, I'd suspect
that Thunderbird is at fault for keeping a bunch of mail in the page
cache.  There are a couple of VM's running though.