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Subject: Re: [mm PATCH v3 2/6] mm: Drop meminit_pfn_in_nid as it is redundant
To:     Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        linux-mm@kvack.org, akpm@linux-foundation.org
Cc:     pavel.tatashin@microsoft.com, mhocko@suse.com,
        dave.jiang@intel.com, linux-kernel@vger.kernel.org,
        willy@infradead.org, davem@davemloft.net,
        yi.z.zhang@linux.intel.com, khalid.aziz@oracle.com,
        rppt@linux.vnet.ibm.com, vbabka@suse.cz,
        sparclinux@vger.kernel.org, dan.j.williams@intel.com,
        ldufour@linux.vnet.ibm.com, mgorman@techsingularity.net,
        mingo@kernel.org, kirill.shutemov@linux.intel.com
References: <20181015202456.2171.88406.stgit@localhost.localdomain>
 <20181015202703.2171.40829.stgit@localhost.localdomain>
From:   Pavel Tatashin <pasha.tatashin@gmail.com>
Message-ID: <a21c1827-10ad-8ff5-c8b6-e34a3f1e8b80@gmail.com>
Date:   Tue, 16 Oct 2018 16:33:10 -0400
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On 10/15/18 4:27 PM, Alexander Duyck wrote:
> As best as I can tell the meminit_pfn_in_nid call is completely redundant.
> The deferred memory initialization is already making use of
> for_each_free_mem_range which in turn will call into __next_mem_range which
> will only return a memory range if it matches the node ID provided assuming
> it is not NUMA_NO_NODE.
> 
> I am operating on the assumption that there are no zones or pgdata_t
> structures that have a NUMA node of NUMA_NO_NODE associated with them. If
> that is the case then __next_mem_range will never return a memory range
> that doesn't match the zone's node ID and as such the check is redundant.
> 
> So one piece I would like to verfy on this is if this works for ia64.
> Technically it was using a different approach to get the node ID, but it
> seems to have the node ID also encoded into the memblock. So I am
> assuming this is okay, but would like to get confirmation on that.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>

If I am not mistaken, this code is for systems with memory interleaving.
Quick looks shows that x86, powerpc, s390, and sparc have it set.

I am not sure about other arches, but at least on SPARC, there are some
processors with memory interleaving feature:

http://www.fujitsu.com/global/products/computing/servers/unix/sparc-enterprise/technology/performance/memory.html

Pavel


> ---
>  mm/page_alloc.c |   50 ++++++++++++++------------------------------------
>  1 file changed, 14 insertions(+), 36 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4bd858d1c3ba..a766a15fad81 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1301,36 +1301,22 @@ int __meminit early_pfn_to_nid(unsigned long pfn)
>  #endif
>  
>  #ifdef CONFIG_NODES_SPAN_OTHER_NODES
> -static inline bool __meminit __maybe_unused
> -meminit_pfn_in_nid(unsigned long pfn, int node,
> -		   struct mminit_pfnnid_cache *state)
> +/* Only safe to use early in boot when initialisation is single-threaded */
> +static inline bool __meminit early_pfn_in_nid(unsigned long pfn, int node)
>  {
>  	int nid;
>  
> -	nid = __early_pfn_to_nid(pfn, state);
> +	nid = __early_pfn_to_nid(pfn, &early_pfnnid_cache);
>  	if (nid >= 0 && nid != node)
>  		return false;
>  	return true;
>  }
>  
> -/* Only safe to use early in boot when initialisation is single-threaded */
> -static inline bool __meminit early_pfn_in_nid(unsigned long pfn, int node)
> -{
> -	return meminit_pfn_in_nid(pfn, node, &early_pfnnid_cache);
> -}
> -
>  #else
> -
>  static inline bool __meminit early_pfn_in_nid(unsigned long pfn, int node)
>  {
>  	return true;
>  }
> -static inline bool __meminit  __maybe_unused
> -meminit_pfn_in_nid(unsigned long pfn, int node,
> -		   struct mminit_pfnnid_cache *state)
> -{
> -	return true;
> -}
>  #endif
>  
>  
> @@ -1459,21 +1445,13 @@ static inline void __init pgdat_init_report_one_done(void)
>   *
>   * Then, we check if a current large page is valid by only checking the validity
>   * of the head pfn.
> - *
> - * Finally, meminit_pfn_in_nid is checked on systems where pfns can interleave
> - * within a node: a pfn is between start and end of a node, but does not belong
> - * to this memory node.
>   */
> -static inline bool __init
> -deferred_pfn_valid(int nid, unsigned long pfn,
> -		   struct mminit_pfnnid_cache *nid_init_state)
> +static inline bool __init deferred_pfn_valid(unsigned long pfn)
>  {
>  	if (!pfn_valid_within(pfn))
>  		return false;
>  	if (!(pfn & (pageblock_nr_pages - 1)) && !pfn_valid(pfn))
>  		return false;
> -	if (!meminit_pfn_in_nid(pfn, nid, nid_init_state))
> -		return false;
>  	return true;
>  }
>  
> @@ -1481,15 +1459,14 @@ static inline void __init pgdat_init_report_one_done(void)
>   * Free pages to buddy allocator. Try to free aligned pages in
>   * pageblock_nr_pages sizes.
>   */
> -static void __init deferred_free_pages(int nid, int zid, unsigned long pfn,
> +static void __init deferred_free_pages(unsigned long pfn,
>  				       unsigned long end_pfn)
>  {
> -	struct mminit_pfnnid_cache nid_init_state = { };
>  	unsigned long nr_pgmask = pageblock_nr_pages - 1;
>  	unsigned long nr_free = 0;
>  
>  	for (; pfn < end_pfn; pfn++) {
> -		if (!deferred_pfn_valid(nid, pfn, &nid_init_state)) {
> +		if (!deferred_pfn_valid(pfn)) {
>  			deferred_free_range(pfn - nr_free, nr_free);
>  			nr_free = 0;
>  		} else if (!(pfn & nr_pgmask)) {
> @@ -1509,17 +1486,18 @@ static void __init deferred_free_pages(int nid, int zid, unsigned long pfn,
>   * by performing it only once every pageblock_nr_pages.
>   * Return number of pages initialized.
>   */
> -static unsigned long  __init deferred_init_pages(int nid, int zid,
> +static unsigned long  __init deferred_init_pages(struct zone *zone,
>  						 unsigned long pfn,
>  						 unsigned long end_pfn)
>  {
> -	struct mminit_pfnnid_cache nid_init_state = { };
>  	unsigned long nr_pgmask = pageblock_nr_pages - 1;
> +	int nid = zone_to_nid(zone);
>  	unsigned long nr_pages = 0;
> +	int zid = zone_idx(zone);
>  	struct page *page = NULL;
>  
>  	for (; pfn < end_pfn; pfn++) {
> -		if (!deferred_pfn_valid(nid, pfn, &nid_init_state)) {
> +		if (!deferred_pfn_valid(pfn)) {
>  			page = NULL;
>  			continue;
>  		} else if (!page || !(pfn & nr_pgmask)) {
> @@ -1582,12 +1560,12 @@ static int __init deferred_init_memmap(void *data)
>  	for_each_free_mem_range(i, nid, MEMBLOCK_NONE, &spa, &epa, NULL) {
>  		spfn = max_t(unsigned long, first_init_pfn, PFN_UP(spa));
>  		epfn = min_t(unsigned long, zone_end_pfn(zone), PFN_DOWN(epa));
> -		nr_pages += deferred_init_pages(nid, zid, spfn, epfn);
> +		nr_pages += deferred_init_pages(zone, spfn, epfn);
>  	}
>  	for_each_free_mem_range(i, nid, MEMBLOCK_NONE, &spa, &epa, NULL) {
>  		spfn = max_t(unsigned long, first_init_pfn, PFN_UP(spa));
>  		epfn = min_t(unsigned long, zone_end_pfn(zone), PFN_DOWN(epa));
> -		deferred_free_pages(nid, zid, spfn, epfn);
> +		deferred_free_pages(spfn, epfn);
>  	}
>  	pgdat_resize_unlock(pgdat, &flags);
>  
> @@ -1676,7 +1654,7 @@ static int __init deferred_init_memmap(void *data)
>  		while (spfn < epfn && nr_pages < nr_pages_needed) {
>  			t = ALIGN(spfn + PAGES_PER_SECTION, PAGES_PER_SECTION);
>  			first_deferred_pfn = min(t, epfn);
> -			nr_pages += deferred_init_pages(nid, zid, spfn,
> +			nr_pages += deferred_init_pages(zone, spfn,
>  							first_deferred_pfn);
>  			spfn = first_deferred_pfn;
>  		}
> @@ -1688,7 +1666,7 @@ static int __init deferred_init_memmap(void *data)
>  	for_each_free_mem_range(i, nid, MEMBLOCK_NONE, &spa, &epa, NULL) {
>  		spfn = max_t(unsigned long, first_init_pfn, PFN_UP(spa));
>  		epfn = min_t(unsigned long, first_deferred_pfn, PFN_DOWN(epa));
> -		deferred_free_pages(nid, zid, spfn, epfn);
> +		deferred_free_pages(spfn, epfn);
>  
>  		if (first_deferred_pfn == epfn)
>  			break;
>