linux-kernel - Re: [PATCH 3/3] mm: move mirrored memory specific code outside of memmap_init

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Date:   Tue, 24 Jul 2018 21:31:18 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kirill.shutemov@...ux.intel.com, Michal Hocko <mhocko@...e.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        dan.j.williams@...el.com, jack@...e.cz, jglisse@...hat.com,
        Souptick Joarder <jrdr.linux@...il.com>, bhe@...hat.com,
        gregkh@...uxfoundation.org, Vlastimil Babka <vbabka@...e.cz>,
        Wei Yang <richard.weiyang@...il.com>, dave.hansen@...el.com,
        rientjes@...gle.com, mingo@...nel.org,
        osalvador@...hadventures.net, abdhalee@...ux.vnet.ibm.com,
        mpe@...erman.id.au
Subject: Re: [PATCH 3/3] mm: move mirrored memory specific code outside of memmap_init_zone

On Tue, Jul 24, 2018 at 9:18 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Tue, 24 Jul 2018 19:55:20 -0400 Pavel Tatashin <pasha.tatashin@...cle.com> wrote:
>
> > memmap_init_zone, is getting complex, because it is called from different
> > contexts: hotplug, and during boot, and also because it must handle some
> > architecture quirks. One of them is mirroed memory.
> >
> > Move the code that decides whether to skip mirrored memory outside of
> > memmap_init_zone, into a separate function.
>
> Conflicts a bit with the page_alloc.c hunk from
> http://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-remain-memblock_next_valid_pfn-on-arm-arm64.patch.  Please check my fixup:

The merge looks good to me. Thank you.

>
> void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>                 unsigned long start_pfn, enum memmap_context context,
>                 struct vmem_altmap *altmap)
> {
>         unsigned long pfn, end_pfn = start_pfn + size;
>         struct page *page;
>
>         if (highest_memmap_pfn < end_pfn - 1)
>                 highest_memmap_pfn = end_pfn - 1;
>
>         /*
>          * Honor reservation requested by the driver for this ZONE_DEVICE
>          * memory
>          */
>         if (altmap && start_pfn == altmap->base_pfn)
>                 start_pfn += altmap->reserve;
>
>         for (pfn = start_pfn; pfn < end_pfn; pfn++) {
>                 /*
>                  * There can be holes in boot-time mem_map[]s handed to this
>                  * function.  They do not exist on hotplugged memory.
>                  */
>                 if (context == MEMMAP_EARLY) {
>                         if (!early_pfn_valid(pfn)) {
>                                 pfn = next_valid_pfn(pfn) - 1;

I wish we did not have to do next_valid_pfn(pfn) - 1, and instead
could do something like:
for (pfn = start_pfn; pfn < end_pfn; pfn = next_valid_pfn(pfn))

Of course the performance of next_valid_pfn() should be optimized on
arm for the common case where next valid pfn is pfn++.

Pavel