linux-kernel - Re: [PATCH 3/3] arm: extend pfn_valid to take into accound freed memory map alignment

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Message-ID: <20210518094427.GR12395@shell.armlinux.org.uk>
Date:   Tue, 18 May 2021 10:44:27 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/3] arm: extend pfn_valid to take into accound freed
 memory map alignment

On Tue, May 18, 2021 at 12:06:13PM +0300, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> When unused memory map is freed the preserved part of the memory map is
> extended to match pageblock boundaries because lots of core mm
> functionality relies on homogeneity of the memory map within pageblock
> boundaries.
> 
> Since pfn_valid() is used to check whether there is a valid memory map
> entry for a PFN, make it return true also for PFNs that have memory map
> entries even if there is no actual memory populated there.

I thought pfn_valid() was a particularly hot path... do we really want
to be doing multiple lookups here? Is there no better solution?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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