linux-kernel - Re: [PATCH] s390/mm: Add missing ctor/dtor on page table upgrade

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Message-ID: <20250124093938.19507-B-hca@linux.ibm.com>
Date: Fri, 24 Jan 2025 10:39:38 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: Kevin Brodsky <kevin.brodsky@....com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] s390/mm: Add missing ctor/dtor on page table upgrade

On Fri, Jan 24, 2025 at 10:29:17AM +0100, Heiko Carstens wrote:
> On Fri, Jan 24, 2025 at 08:58:07AM +0100, Kevin Brodsky wrote:
> In addition, looking at [1] where page table accounting was introduced: it
> is really meant to reflect the memory consumption used by page tables. This
> might work for nearly all architectures which have the same page table size
> for every level; but on s390 the lowest level comes with 4kb page tables
> while all other levels come with 16kb page tables.
> 
> Therefore at least on s390 you really can't tell how much memory is
> consumed by page tables by only looking at nr_page_table_pages. It _might_
> make sense to introduce a factor of four for page table accounting for
> higher levels, so those numbers make at least some sense; but not sure
> about that.

Ah, this is actually not true at all, since we have

static inline void __lruvec_stat_add_folio(struct folio *folio,
                                           enum node_stat_item idx)
{
	__lruvec_stat_mod_folio(folio, idx, folio_nr_pages(folio));
}

which will do exactly what we want. So this part is not a problem.