Message-Id: <20250709110648.52688-1-sj@kernel.org>
Date: Wed,  9 Jul 2025 04:06:48 -0700
From: SeongJae Park <sj@...nel.org>
To: Bijan Tabatabai <bijan311@...il.com>
Cc: SeongJae Park <sj@...nel.org>,
	damon@...ts.linux.dev,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org,
	akpm@...ux-foundation.org,
	corbet@....net,
	bijantabatab@...ron.com,
	venkataravis@...ron.com,
	emirakhur@...ron.com,
	vtavarespetr@...ron.com,
	ajayjoshi@...ron.com,
	bijan <bijan@...e0.bijan-262664.superpages-pg0.wisc.cloudlab.us>
Subject: Re: [PATCH v4 00/13] mm/damon/vaddr: Allow interleaving in migrate_{hot,cold} actions

On Tue,  8 Jul 2025 19:59:30 -0500 Bijan Tabatabai <bijan311@...il.com> wrote:

> From: bijan <bijan@...e0.bijan-262664.superpages-pg0.wisc.cloudlab.us>

Maybe this is not an intended part but something from misconfiguration?  I show
Andrew merged this series into mm-new after removing this, but headsup for a
case that we might do rebase.

> 
> A recent patch set automatically sets the interleave weight for each node
> according to the node's maximum bandwidth [1]. In another thread, the patch
> set's author, Joshua Hahn, wondered if/how thes weights should be changed
> if the bandwidth utilization of the system changes [2].
> 
> This patch set adds the mechanism for dynamically changing how application
> data is interleaved across nodes while leaving the policy of what the
> interleave weights should be to userspace. It does this by having the
> migrate_{hot,cold} operating schemes interleave application data according
> to the list of migration nodes and weights passed in via the DAMON sysfs
> interface. This functionality can be used to dynamically adjust how folios
> are interleaved by having a userspace process adjust those weights. If no
> specific destination nodes or weights are provided, the migrate_{hot,cold}
> actions will only migrate folios to damos->target_nid as before.
> 
> The algorithm used to interleave the folios is similar to the one used for
> the weighted interleave mempolicy [3]. It uses the offset from which a
> folio is mapped into a VMA to determine the node the folio should be placed
> in. This method is convenient because for a given set of interleave
> weights, a folio has only one valid node it can be placed in, limitng the
> amount of unnecessary data movement. However, finding out how a folio is
> mapped inside of a VMA requires a costly rmap walk when using a paddr
> scheme. As such, we have decided that this functionality makes more sense
> as a vaddr scheme [4]. To this end, this patch set also adds vaddr versions
> of the migrate_{hot,cold}.
[...]
> Revision History
> ================
> Changes from v3 [10]:
> - Fix bug where huge pages would be split

Maybe "walk->action = ACTION_CONTINUE;" of ninth patch?  Nice finding!

Nontheless, since this was found by you and didn't discussed in public before,
it would be nice to add a short additional clarifications like above, if we
(unlikely) do rebase.

> - Fix code nits/issues SJ pointed out
> - Added SJ's Reviewed-by tag where appropriate

Thank you for revisioning :)

> 
> Changes from v2 [11]:
> - Implement interleaving using vaddr instead of paddr
> - Add vaddr implementation of migrate_{hot,cold}
> - Use DAMON specific interleave weights instead of mempolicy weights
> 
> Changes from v1 [12]:
> - Reuse migrate_{hot,cold} actions instead of creating a new action
> - Remove vaddr implementation
> - Remove most of the use of mempolicy, instead duplicate the interleave
>   logic and access interleave weights directly
> - Write more about the use case in the cover letter
> - Write about why DAMON was used for this in the cover letter
> - Add correctness test to the cover letter
> - Add performance test
> 
> [1] https://lore.kernel.org/linux-mm/20250520141236.2987309-1-joshua.hahnjy@gmail.com/
> [2] https://lore.kernel.org/linux-mm/20250313155705.1943522-1-joshua.hahnjy@gmail.com/
> [3] https://elixir.bootlin.com/linux/v6.15.4/source/mm/mempolicy.c#L2015
> [4] https://lore.kernel.org/damon/20250624223310.55786-1-sj@kernel.org/
> [5] https://lore.kernel.org/linux-mm/20250314151137.892379-1-joshua.hahnjy@gmail.com/
> [6] https://lore.kernel.org/linux-mm/87frjfx6u4.fsf@DESKTOP-5N7EMDA/
> [7] https://github.com/SNU-ARC/MERCI
> [8] https://lore.kernel.org/damon/20250702051558.54138-1-sj@kernel.org/
> [9] https://lore.kernel.org/damon/20250709004729.17252-1-bijan311@gmail.com/
> [10] https://lore.kernel.org/damon/20250702201337.5780-1-bijan311@gmail.com/
> [11] https://lore.kernel.org/damon/20250620180458.5041-1-bijan311@gmail.com/
> [12] https://lore.kernel.org/linux-mm/20250612181330.31236-1-bijan311@gmail.com/
> 
> Bijan Tabatabai (7):
>   mm/damon/core: Commit damos->migrate_dests
>   mm/damon: Move migration helpers from paddr to ops-common
>   mm/damon/vaddr: Add vaddr versions of migrate_{hot,cold}
>   Docs/mm/damon/design: Document vaddr support for migrate_{hot,cold}
>   mm/damon/vaddr: Use damos->migrate_dests in migrate_{hot,cold}
>   mm/damon: Move folio filtering from paddr to ops-common
>   mm/damon/vaddr: Apply filters in migrate_{hot/cold}
> 
> SeongJae Park (6):
>   mm/damon: add struct damos_migrate_dests
>   mm/damon/core: add damos->migrate_dests field
>   mm/damon/sysfs-schemes: implement DAMOS action destinations directory
>   mm/damon/sysfs-schemes: set damos->migrate_dests
>   Docs/ABI/damon: document schemes dests directory
>   Docs/admin-guide/mm/damon/usage: document dests directory

For the entire series,

Reviewed-by: SeongJae Park <sj@...nel.org>


Thanks,
SJ

[...]

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