linux-kernel - Re: [PATCH] mm: use mem_map_offset instead of mem_map

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Message-ID: <Yxd9tA8ThZtB77dq@monkey>
Date:   Tue, 6 Sep 2022 10:04:52 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Cheng Li <lic121@...natelecom.cn>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: use mem_map_offset instead of mem_map_next

On 09/04/22 22:15, Matthew Wilcox wrote:
> On Sun, Sep 04, 2022 at 02:02:41PM +0000, Cheng Li wrote:
> > To handle discontiguity case, mem_map_next() has a parameter named
> > `offset`. As a function caller, one would be confused why "get
> > next entry" needs a parameter named "offset". The other drawback of
> > mem_map_next() is that the callers must take care of the map between
> > parameter "iter" and "offset", otherwise we may get an hole or
> > duplication during iteration. So we use mem_map_offset instead of
> > mem_map_next.
> 
> I think we should go further and get rid of mem_map_offset().
> nth_page() is now more efficient than mem_map_offset().

Agree.

However, IIUC nth_page() will 'almost' always be more efficient.  The
only exception is unlikely configuration where CONFIG_SPARSEMEM &&
!CONFIG_SPARSEMEM_VMEMMAP.  Correct?

Not arguing against replacement.  Just wanting to refresh my memory.
-- 
Mike Kravetz