Re: + mm-split-deferred_init_range-into-initializing-and-freeing-parts.patch added to -mm tree

Re: + mm-split-deferred_init_range-into-initializing-and-freeing-parts.patch added to -mm tree

[Michal Hocko]

On Tue 21-11-17 15:44:51, Andrew Morton wrote:
> ------------------------------------------------------
> From: Pavel Tatashin <pasha.tatashin@oracle.com>
> Subject: mm: split deferred_init_range into initializing and freeing parts
> 
> In deferred_init_range() we initialize struct pages, and also free them to
> buddy allocator.  We do it in separate loops, because buddy page is
> computed ahead, so we do not want to access a struct page that has not
> been initialized yet.
> 
> There is still, however, a corner case where it is potentially possible to
> access uninitialized struct page: this is when buddy page is from the next
> memblock range.
> 
> This patch fixes this problem by splitting deferred_init_range() into two
> functions: one to initialize struct pages, and another to free them.
> 
> In addition, this patch brings the following improvements:
> - Get rid of __def_free() helper function. And simplifies loop logic by
>   adding a new pfn validity check function: deferred_pfn_valid().
> - Reduces number of variables that we track. So, there is a higher chance
>   that we will avoid using stack to store/load variables inside hot loops.
> - Enables future multi-threading of these functions: do initialization in
>   multiple threads, wait for all threads to finish, do freeing part in
>   multithreading.
> 
> Tested on x86 with 1T of memory to make sure no regressions are introduced.

I thought I have acked this one. Let me dig that out.
...
Ohh, here it is https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1528267.html

> 
> Link: http://lkml.kernel.org/r/20171107150446.32055-2-pasha.tatashin@oracle.com
> Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Steven Sistare <steven.sistare@oracle.com>
> Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> 
>  mm/page_alloc.c |  146 +++++++++++++++++++++++-----------------------
>  1 file changed, 76 insertions(+), 70 deletions(-)
> 
> diff -puN mm/page_alloc.c~mm-split-deferred_init_range-into-initializing-and-freeing-parts mm/page_alloc.c
> --- a/mm/page_alloc.c~mm-split-deferred_init_range-into-initializing-and-freeing-parts
> +++ a/mm/page_alloc.c
> @@ -1457,92 +1457,87 @@ static inline void __init pgdat_init_rep
>  }
>  
>  /*
> - * Helper for deferred_init_range, free the given range, reset the counters, and
> - * return number of pages freed.
> + * Returns true if page needs to be initialized of freed to buddy allocator.
> + *
> + * First we check if pfn is valid on architectures where it is possible to have
> + * holes within pageblock_nr_pages. On systems where it is not possible, this
> + * function is optimized out.
> + *
> + * 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 unsigned long __init __def_free(unsigned long *nr_free,
> -					      unsigned long *free_base_pfn,
> -					      struct page **page)
> +static inline bool __init
> +deferred_pfn_valid(int nid, unsigned long pfn,
> +		   struct mminit_pfnnid_cache *nid_init_state)
>  {
> -	unsigned long nr = *nr_free;
> +	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;
> +}
>  
> -	deferred_free_range(*free_base_pfn, nr);
> -	*free_base_pfn = 0;
> -	*nr_free = 0;
> -	*page = NULL;
> +/*
> + * 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,
> +				       unsigned long end_pfn)
> +{
> +	struct mminit_pfnnid_cache nid_init_state = { };
> +	unsigned long nr_pgmask = pageblock_nr_pages - 1;
> +	unsigned long nr_free = 0;
>  
> -	return nr;
> +	for (; pfn < end_pfn; pfn++) {
> +		if (!deferred_pfn_valid(nid, pfn, &nid_init_state)) {
> +			deferred_free_range(pfn - nr_free, nr_free);
> +			nr_free = 0;
> +		} else if (!(pfn & nr_pgmask)) {
> +			deferred_free_range(pfn - nr_free, nr_free);
> +			nr_free = 1;
> +			cond_resched();
> +		} else {
> +			nr_free++;
> +		}
> +	}
> +	/* Free the last block of pages to allocator */
> +	deferred_free_range(pfn - nr_free, nr_free);
>  }
>  
> -static unsigned long __init deferred_init_range(int nid, int zid,
> -						unsigned long start_pfn,
> -						unsigned long end_pfn)
> +/*
> + * Initialize struct pages.  We minimize pfn page lookups and scheduler checks
> + * 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,
> +						 unsigned long pfn,
> +						 unsigned long end_pfn)
>  {
>  	struct mminit_pfnnid_cache nid_init_state = { };
>  	unsigned long nr_pgmask = pageblock_nr_pages - 1;
> -	unsigned long free_base_pfn = 0;
>  	unsigned long nr_pages = 0;
> -	unsigned long nr_free = 0;
>  	struct page *page = NULL;
> -	unsigned long pfn;
>  
> -	/*
> -	 * First we check if pfn is valid on architectures where it is possible
> -	 * to have holes within pageblock_nr_pages. On systems where it is not
> -	 * possible, this function is optimized out.
> -	 *
> -	 * Then, we check if a current large page is valid by only checking the
> -	 * validity of the head pfn.
> -	 *
> -	 * 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.
> -	 *
> -	 * Finally, we minimize pfn page lookups and scheduler checks by
> -	 * performing it only once every pageblock_nr_pages.
> -	 *
> -	 * We do it in two loops: first we initialize struct page, than free to
> -	 * buddy allocator, becuse while we are freeing pages we can access
> -	 * pages that are ahead (computing buddy page in __free_one_page()).
> -	 */
> -	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> -		if (!pfn_valid_within(pfn))
> +	for (; pfn < end_pfn; pfn++) {
> +		if (!deferred_pfn_valid(nid, pfn, &nid_init_state)) {
> +			page = NULL;
>  			continue;
> -		if ((pfn & nr_pgmask) || pfn_valid(pfn)) {
> -			if (meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
> -				if (page && (pfn & nr_pgmask))
> -					page++;
> -				else
> -					page = pfn_to_page(pfn);
> -				__init_single_page(page, pfn, zid, nid);
> -				cond_resched();
> -			}
> -		}
> -	}
> -
> -	page = NULL;
> -	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
> -		if (!pfn_valid_within(pfn)) {
> -			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> -		} else if (!(pfn & nr_pgmask) && !pfn_valid(pfn)) {
> -			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> -		} else if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
> -			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> -		} else if (page && (pfn & nr_pgmask)) {
> -			page++;
> -			nr_free++;
> -		} else {
> -			nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> +		} else if (!page || !(pfn & nr_pgmask)) {
>  			page = pfn_to_page(pfn);
> -			free_base_pfn = pfn;
> -			nr_free = 1;
>  			cond_resched();
> +		} else {
> +			page++;
>  		}
> +		__init_single_page(page, pfn, zid, nid);
> +		nr_pages++;
>  	}
> -	/* Free the last block of pages to allocator */
> -	nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> -
> -	return nr_pages;
> +	return (nr_pages);
>  }
>  
>  /* Initialise remaining memory on a node */
> @@ -1582,10 +1577,21 @@ static int __init deferred_init_memmap(v
>  	}
>  	first_init_pfn = max(zone->zone_start_pfn, first_init_pfn);
>  
> +	/*
> +	 * Initialize and free pages. We do it in two loops: first we initialize
> +	 * struct page, than free to buddy allocator, because while we are
> +	 * freeing pages we can access pages that are ahead (computing buddy
> +	 * page in __free_one_page()).
> +	 */
> +	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);
> +	}
>  	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_range(nid, zid, spfn, epfn);
> +		deferred_free_pages(nid, zid, spfn, epfn);
>  	}
>  
>  	/* Sanity check that the next zone really is unpopulated */
> _
> 
> Patches currently in -mm which might be from pasha.tatashin@oracle.com are
> 
> mm-relax-deferred-struct-page-requirements.patch
> mm-split-deferred_init_range-into-initializing-and-freeing-parts.patch
> sparc64-ng4-memset-32-bits-overflow.patch

-- 
Michal Hocko
SUSE Labs

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