linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Ingo Molnar <mingo@kernel.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Raghavendra K T <raghavendra.kt@amd.com>,
	K Prateek Nayak <kprateek.nayak@amd.com>,
	Bharata B Rao <bharata@amd.com>, Ingo Molnar <mingo@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH 6/6] sched/numa: Complete scanning of inactive VMAs when there is no alternative
Date: Tue, 10 Oct 2023 23:39:44 +0200	[thread overview]
Message-ID: <ZSXEoLzHhwhO1t3k@gmail.com> (raw)
In-Reply-To: <20231010095752.yueqcseg7p3xg5ui@techsingularity.net>


* Mel Gorman <mgorman@techsingularity.net> wrote:

> > 64 (BITS_PER_LONG) feels a bit small, especially on larger machines running 
> > threaded workloads, and the kmalloc of numab_state likely allocates a full 
> > cacheline anyway, so we could double the hash size from 8 bytes (2x1 longs) 
                                                            ^--- 16 bytes
> > to 32 bytes (2x2 longs) with very little real cost, and still have a long 
> > field left to spare?
> > 
> 
> You're right, we could and it's relatively cheap. I would worry that as 
> the storage overhead is per-VMA then workloads for large machines may 
> also have lots of VMAs that are not necessarily using threads.

So I think there would be *zero* extra per-vma storage overhead, because 
vma->numab_state is a pointer, with the structure kmalloc() allocated, 
which should round the allocation to cacheline granularity anyway: 64 bytes 
on NUMA systems that matter.

So with the current size of 'struct vma_numab_state' of 36 bytes, we can 
extend it by 16 bytes with zero additional storage cost.

And since there's no cost, and less hash collisions are always good, the 
change wouldn't need any other justification. :-)

[ Plus the resulting abstraction for the definition of a larger bitmask 
  would probably make future extensions easier. ]

But ... it was just a suggestion.

Thanks,

	Ingo

  reply	other threads:[~2023-10-10 21:39 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-10-10  8:31 [PATCH 0/6] sched/numa: Complete scanning of partial and inactive VMAs Mel Gorman
2023-10-10  8:31 ` [PATCH 1/6] sched/numa: Document vma_numab_state fields Mel Gorman
2023-10-10  9:43   ` [tip: sched/core] " tip-bot2 for Mel Gorman
2023-10-10  8:31 ` [PATCH 2/6] sched/numa: Rename vma_numab_state.access_pids Mel Gorman
2023-10-10  9:43   ` [tip: sched/core] sched/numa: Rename vma_numab_state::access_pids[] => ::pids_active[], ::next_pid_reset => ::pids_active_reset tip-bot2 for Mel Gorman
2023-10-10  8:31 ` [PATCH 3/6] sched/numa: Trace decisions related to skipping VMAs Mel Gorman
2023-10-10  9:43   ` [tip: sched/core] " tip-bot2 for Mel Gorman
2023-10-10  8:31 ` [PATCH 4/6] sched/numa: Move up the access pid reset logic Mel Gorman
2023-10-10  9:43   ` [tip: sched/core] " tip-bot2 for Raghavendra K T
2023-10-10  8:31 ` [PATCH 5/6] sched/numa: Complete scanning of partial VMAs regardless of PID activity Mel Gorman
2023-10-10  9:43   ` [tip: sched/core] " tip-bot2 for Mel Gorman
2023-10-10 21:47   ` tip-bot2 for Mel Gorman
2023-10-10  8:31 ` [PATCH 6/6] sched/numa: Complete scanning of inactive VMAs when there is no alternative Mel Gorman
2023-10-10  9:23   ` Ingo Molnar
2023-10-10  9:57     ` Mel Gorman
2023-10-10 21:39       ` Ingo Molnar [this message]
2023-10-10 11:40     ` Raghavendra K T
2024-02-24  4:50       ` Raghavendra K T
2023-10-10  9:43   ` [tip: sched/core] " tip-bot2 for Mel Gorman
2023-10-10 11:42   ` [PATCH 6/6] " Raghavendra K T
2023-10-10 21:47   ` [tip: sched/core] " tip-bot2 for Mel Gorman
2023-10-10 11:39 ` [PATCH 0/6] sched/numa: Complete scanning of partial and inactive VMAs Raghavendra K T
2023-10-10 21:45   ` Ingo Molnar

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=ZSXEoLzHhwhO1t3k@gmail.com \
    --to=mingo@kernel.org \
    --cc=bharata@amd.com \
    --cc=kprateek.nayak@amd.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mgorman@techsingularity.net \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=raghavendra.kt@amd.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).