linux-kernel - Re: [PATCH v1 0/2] Ignore non-LRU-based reclaim in memcg reclaim

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Date:   Wed, 8 Mar 2023 23:08:20 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        Peter Xu <peterx@...hat.com>, NeilBrown <neilb@...e.de>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 0/2] Ignore non-LRU-based reclaim in memcg reclaim

On Thu, Mar 09, 2023 at 08:25:29AM +1100, Dave Chinner wrote:
> On Wed, Mar 08, 2023 at 12:24:08PM -0800, Yosry Ahmed wrote:
> > > I tried to come up with something better, but wasn't happy with any of
> > > the options, either. So I defaulted to just leaving it alone :-)
> > >
> > > It's part of the shrinker API and the name hasn't changed since the
> > > initial git import of the kernel tree. It should be fine, churn-wise.
> > 
> > Last attempt, just update_reclaim_state() (corresponding to
> > flush_reclaim_state() below). It doesn't tell a story, but neither
> > does incrementing a counter in current->reclaim_state. If that doesn't
> > make you happy I'll give up now and leave it as-is :)
> 
> This is used in different subsystem shrinkers outside mm/, so the
> name needs to be correctly namespaced. Please prefix it with the
> subsystem the function belongs to, at minimum.
> 
> mm_account_reclaimed_pages() is what is actually being done here.
> It is self describing  and leaves behind no ambiguity as to what is
> being accounted and why, nor which subsystem the accounting belongs
> to.
> 
> It doesn't matter what the internal mm/vmscan structures are called,
> all we care about is telling the mm infrastructure how many extra
> pages were freed by the shrinker....

My first preference would still be to just leave it. IMO that one line
saved in a small handful of places isn't worth the indirection,
obscuring the `current' deref etc.

But mm_account_reclaimed_pages() works for me if you really want to
enapsulate it.