Subject: Re: [PATCH v2 17/20] mm: free_area_init: allow defining max_zone_pfn in descending order

From: Mike Rapoport <[email-masked]>
Date: Tue, 5 May 2020 16:45:01 +0300

On Tue, May 05, 2020 at 06:18:11AM -0700, Guenter Roeck wrote:
> On 5/4/20 8:39 AM, Mike Rapoport wrote:
> > On Sun, May 03, 2020 at 11:43:00AM -0700, Guenter Roeck wrote:
> >> On Sun, May 03, 2020 at 10:41:38AM -0700, Guenter Roeck wrote:
> >>> Hi,
> >>>
> >>> On Wed, Apr 29, 2020 at 03:11:23PM +0300, Mike Rapoport wrote:
> >>>> From: Mike Rapoport <[email-masked]>
> >>>>
> >>>> Some architectures (e.g. ARC) have the ZONE_HIGHMEM zone below the
> >>>> ZONE_NORMAL. Allowing free_area_init() parse max_zone_pfn array even it is
> >>>> sorted in descending order allows using free_area_init() on such
> >>>> architectures.
> >>>>
> >>>> Add top -> down traversal of max_zone_pfn array in free_area_init() and use
> >>>> the latter in ARC node/zone initialization.
> >>>>
> >>>> Signed-off-by: Mike Rapoport <[email-masked]>
> >>>
> >>> This patch causes my microblazeel qemu boot test in linux-next to fail.
> >>> Reverting it fixes the problem.
> >>>
> >> The same problem is seen with s390 emulations.
> > 
> > Yeah, this patch breaks some others as well :(
> > 
> > My assumption that max_zone_pfn defines architectural limit for maximal
> > PFN that can belong to a zone was over-optimistic. Several arches
> > actually do that, but others do
> > 
> > 	max_zone_pfn[ZONE_DMA] = MAX_DMA_PFN;
> > 	max_zone_pfn[ZONE_NORMAL] = max_pfn;
> > 
> > where MAX_DMA_PFN is build-time constrain and max_pfn is run time limit
> > for the current system.
> > 
> > So, when max_pfn is lower than MAX_DMA_PFN, the free_init_area() will
> > consider max_zone_pfn as descending and will wrongly calculate zone
> > extents.
> > 
> > That said, instead of trying to create a generic way to special case
> > ARC, I suggest to simply use the below patch instead.
> > 
> 
> As a reminder, I reported the problem against s390 and microblazeel
> (interestingly enough, microblaze (big endian) works), not against arc.

With this fix microblazeel and s390 worked for me and also Christian had
reported that s390 is fixed.

microblaze (big endian) works because its defconfig does not enable HIGHMEM
while little endian does.

ARC is mentioned because it is the only arch that may have ZONE_HIGHMEM
and ZONE_NORMAL and this patch was required to consolidate
free_area_init* variants.

> Guenter
> 
> > diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
> > index 41eb9be1653c..386959bac3d2 100644
> > --- a/arch/arc/mm/init.c
> > +++ b/arch/arc/mm/init.c
> > @@ -77,6 +77,11 @@ void __init early_init_dt_add_memory_arch(u64 base, u64 size)
> >  		base, TO_MB(size), !in_use ? "Not used":"");
> >  }
> >  
> > +bool arch_has_descending_max_zone_pfns(void)
> > +{
> > +	return true;
> > +}
> > +
> >  /*
> >   * First memory setup routine called from setup_arch()
> >   * 1. setup swapper's mm @init_mm
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index b990e9734474..114f0e027144 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -7307,6 +7307,15 @@ static void check_for_memory(pg_data_t *pgdat, int nid)
> >  	}
> >  }
> >  
> > +/*
> > + * Some architecturs, e.g. ARC may have ZONE_HIGHMEM below ZONE_NORMAL. For
> > + * such cases we allow max_zone_pfn sorted in the descending order
> > + */
> > +bool __weak arch_has_descending_max_zone_pfns(void)
> > +{
> > +	return false;
> > +}
> > +
> >  /**
> >   * free_area_init - Initialise all pg_data_t and zone data
> >   * @max_zone_pfn: an array of max PFNs for each zone
> > @@ -7324,7 +7333,7 @@ void __init free_area_init(unsigned long *max_zone_pfn)
> >  {
> >  	unsigned long start_pfn, end_pfn;
> >  	int i, nid, zone;
> > -	bool descending = false;
> > +	bool descending;
> >  
> >  	/* Record where the zone boundaries are */
> >  	memset(arch_zone_lowest_possible_pfn, 0,
> > @@ -7333,14 +7342,7 @@ void __init free_area_init(unsigned long *max_zone_pfn)
> >  				sizeof(arch_zone_highest_possible_pfn));
> >  
> >  	start_pfn = find_min_pfn_with_active_regions();
> > -
> > -	/*
> > -	 * Some architecturs, e.g. ARC may have ZONE_HIGHMEM below
> > -	 * ZONE_NORMAL. For such cases we allow max_zone_pfn sorted in the
> > -	 * descending order
> > -	 */
> > -	if (MAX_NR_ZONES > 1 && max_zone_pfn[0] > max_zone_pfn[1])
> > -		descending = true;
> > +	descending = arch_has_descending_max_zone_pfns();
> >  
> >  	for (i = 0; i < MAX_NR_ZONES; i++) {
> >  		if (descending)
> > 
> >> Guenter
> >>
> >>> qemu command line:
> >>>
> >>> qemu-system-microblazeel -M petalogix-ml605 -m 256 \
> >>> 	-kernel arch/microblaze/boot/linux.bin -no-reboot \
> >>> 	-initrd rootfs.cpio \
> >>> 	-append 'panic=-1 slub_debug=FZPUA rdinit=/sbin/init console=ttyS0,115200' \
> >>> 	-monitor none -serial stdio -nographic
> >>>
> >>> initrd:
> >>> 	https://github.com/groeck/linux-build-test/blob/master/rootfs/microblazeel/rootfs.cpio.gz
> >>> configuration:
> >>> 	https://github.com/groeck/linux-build-test/blob/master/rootfs/microblazeel/qemu_microblazeel_ml605_defconfig
> >>>
> >>> Bisect log is below.
> >>>
> >>> Guenter
> >>>
> >>> ---
> >>> # bad: [fb9d670f57e3f6478602328bbbf71138be06ca4f] Add linux-next specific files for 20200501
> >>> # good: [6a8b55ed4056ea5559ebe4f6a4b247f627870d4c] Linux 5.7-rc3
> >>> git bisect start 'HEAD' 'v5.7-rc3'
> >>> # good: [068b80b68a670f0b17288c8a3d1ee751f35162ab] Merge remote-tracking branch 'drm/drm-next'
> >>> git bisect good 068b80b68a670f0b17288c8a3d1ee751f35162ab
> >>> # good: [46c70fc6a3ac35cd72ddad248dcbe4eee716d2a5] Merge remote-tracking branch 'drivers-x86/for-next'
> >>> git bisect good 46c70fc6a3ac35cd72ddad248dcbe4eee716d2a5
> >>> # good: [f39c4ad479a2f005f972a2b941b40efa6b9c9349] Merge remote-tracking branch 'rpmsg/for-next'
> >>> git bisect good f39c4ad479a2f005f972a2b941b40efa6b9c9349
> >>> # bad: [165d3ee0162fe28efc2c8180176633e33515df15] ipc-convert-ipcs_idr-to-xarray-update
> >>> git bisect bad 165d3ee0162fe28efc2c8180176633e33515df15
> >>> # good: [001f1d211ed2ed0f005838dc4390993930bbbd69] mm: remove early_pfn_in_nid() and CONFIG_NODES_SPAN_OTHER_NODES
> >>> git bisect good 001f1d211ed2ed0f005838dc4390993930bbbd69
> >>> # bad: [aaad7401bd32f10c1d591dd886b3a9b9595c6d77] mm/vmsan: fix some typos in comment
> >>> git bisect bad aaad7401bd32f10c1d591dd886b3a9b9595c6d77
> >>> # bad: [09f9d0ab1fbed85623b283995aa7a7d78daa1611] khugepaged: allow to collapse PTE-mapped compound pages
> >>> git bisect bad 09f9d0ab1fbed85623b283995aa7a7d78daa1611
> >>> # bad: [c942fc8a3e5088407bc32d94f554bab205175f8a] mm/vmstat.c: do not show lowmem reserve protection information of empty zone
> >>> git bisect bad c942fc8a3e5088407bc32d94f554bab205175f8a
> >>> # bad: [b29358d269ace3826d8521bea842fc2984cfc11b] mm/page_alloc.c: rename free_pages_check() to check_free_page()
> >>> git bisect bad b29358d269ace3826d8521bea842fc2984cfc11b
> >>> # bad: [be0fb591a1f1df20a00c8f023f9ca4891f177b0d] mm: simplify find_min_pfn_with_active_regions()
> >>> git bisect bad be0fb591a1f1df20a00c8f023f9ca4891f177b0d
> >>> # bad: [c17422a008d36dcf3e9f51469758c5762716cb0a] mm: rename free_area_init_node() to free_area_init_memoryless_node()
> >>> git bisect bad c17422a008d36dcf3e9f51469758c5762716cb0a
> >>> # bad: [51a2f644fd020d5f090044825c388444d11029d5] mm: free_area_init: allow defining max_zone_pfn in descending order
> >>> git bisect bad 51a2f644fd020d5f090044825c388444d11029d5
> >>> # first bad commit: [51a2f644fd020d5f090044825c388444d11029d5] mm: free_area_init: allow defining max_zone_pfn in descending order
> > 
> 

-- 
Sincerely yours,
Mike.