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SubjectRe: [PATCH v12 01/11] mm: deferred_init_memmap improvements
On Fri 13-10-17 13:32:04, Pavel Tatashin wrote:
> deferred_init_memmap() is called when struct pages are initialized later
> in boot by slave CPUs. This patch simplifies and optimizes this function,
> and also fixes a couple issues (described below).
>
> The main change is that now we are iterating through free memblock areas
> instead of all configured memory. Thus, we do not have to check if the
> struct page has already been initialized.
>
> =====
> In deferred_init_memmap() where all deferred struct pages are initialized
> we have a check like this:
>
> if (page->flags) {
> VM_BUG_ON(page_zone(page) != zone);
> goto free_range;
> }
>
> This way we are checking if the current deferred page has already been
> initialized. It works, because memory for struct pages has been zeroed, and
> the only way flags are not zero if it went through __init_single_page()
> before. But, once we change the current behavior and won't zero the memory
> in memblock allocator, we cannot trust anything inside "struct page"es
> until they are initialized. This patch fixes this.
>
> The deferred_init_memmap() is re-written to loop through only free memory
> ranges provided by memblock.
>
> Note, this first issue is relevant only when the following change is
> merged:
>
> =====
> This patch fixes another existing issue on systems that have holes in
> zones i.e CONFIG_HOLES_IN_ZONE is defined.
>
> In for_each_mem_pfn_range() we have code like this:
>
> if (!pfn_valid_within(pfn)
> goto free_range;
>
> Note: 'page' is not set to NULL and is not incremented but 'pfn' advances.
> Thus means if deferred struct pages are enabled on systems with these kind
> of holes, linux would get memory corruptions. I have fixed this issue by
> defining a new macro that performs all the necessary operations when we
> free the current set of pages.

This really begs to have two patches... I will not insist though. I also
suspect the code can be further simplified but again this is nothing to
block this to go.

> Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
> Reviewed-by: Steven Sistare <steven.sistare@oracle.com>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
> Reviewed-by: Bob Picco <bob.picco@oracle.com>

I do not see any obvious issues in the patch

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

> ---
> mm/page_alloc.c | 168 ++++++++++++++++++++++++++++----------------------------
> 1 file changed, 85 insertions(+), 83 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 77e4d3c5c57b..cdbd14829fd3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1410,14 +1410,17 @@ void clear_zone_contiguous(struct zone *zone)
> }
>
> #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> -static void __init deferred_free_range(struct page *page,
> - unsigned long pfn, int nr_pages)
> +static void __init deferred_free_range(unsigned long pfn,
> + unsigned long nr_pages)
> {
> - int i;
> + struct page *page;
> + unsigned long i;
>
> - if (!page)
> + if (!nr_pages)
> return;
>
> + page = pfn_to_page(pfn);
> +
> /* Free a large naturally-aligned chunk if possible */
> if (nr_pages == pageblock_nr_pages &&
> (pfn & (pageblock_nr_pages - 1)) == 0) {
> @@ -1443,19 +1446,89 @@ static inline void __init pgdat_init_report_one_done(void)
> complete(&pgdat_init_all_done_comp);
> }
>
> +/*
> + * Helper for deferred_init_range, free the given range, reset the counters, and
> + * return number of pages freed.
> + */
> +static inline unsigned long __def_free(unsigned long *nr_free,
> + unsigned long *free_base_pfn,
> + struct page **page)
> +{
> + unsigned long nr = *nr_free;
> +
> + deferred_free_range(*free_base_pfn, nr);
> + *free_base_pfn = 0;
> + *nr_free = 0;
> + *page = NULL;
> +
> + return nr;
> +}
> +
> +static unsigned long deferred_init_range(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;
> +
> + for (; pfn < end_pfn; 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.
> + */
> + 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++;
> + __init_single_page(page, pfn, zid, nid);
> + nr_free++;
> + } else {
> + nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> + page = pfn_to_page(pfn);
> + __init_single_page(page, pfn, zid, nid);
> + free_base_pfn = pfn;
> + nr_free = 1;
> + cond_resched();
> + }
> + }
> + /* Free the last block of pages to allocator */
> + nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> +
> + return nr_pages;
> +}
> +
> /* Initialise remaining memory on a node */
> static int __init deferred_init_memmap(void *data)
> {
> pg_data_t *pgdat = data;
> int nid = pgdat->node_id;
> - struct mminit_pfnnid_cache nid_init_state = { };
> unsigned long start = jiffies;
> unsigned long nr_pages = 0;
> - unsigned long walk_start, walk_end;
> - int i, zid;
> + unsigned long spfn, epfn;
> + phys_addr_t spa, epa;
> + int zid;
> struct zone *zone;
> unsigned long first_init_pfn = pgdat->first_deferred_pfn;
> const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
> + u64 i;
>
> if (first_init_pfn == ULONG_MAX) {
> pgdat_init_report_one_done();
> @@ -1477,83 +1550,12 @@ static int __init deferred_init_memmap(void *data)
> if (first_init_pfn < zone_end_pfn(zone))
> break;
> }
> + first_init_pfn = max(zone->zone_start_pfn, first_init_pfn);
>
> - for_each_mem_pfn_range(i, nid, &walk_start, &walk_end, NULL) {
> - unsigned long pfn, end_pfn;
> - struct page *page = NULL;
> - struct page *free_base_page = NULL;
> - unsigned long free_base_pfn = 0;
> - int nr_to_free = 0;
> -
> - end_pfn = min(walk_end, zone_end_pfn(zone));
> - pfn = first_init_pfn;
> - if (pfn < walk_start)
> - pfn = walk_start;
> - if (pfn < zone->zone_start_pfn)
> - pfn = zone->zone_start_pfn;
> -
> - for (; pfn < end_pfn; pfn++) {
> - if (!pfn_valid_within(pfn))
> - goto free_range;
> -
> - /*
> - * Ensure pfn_valid is checked every
> - * pageblock_nr_pages for memory holes
> - */
> - if ((pfn & (pageblock_nr_pages - 1)) == 0) {
> - if (!pfn_valid(pfn)) {
> - page = NULL;
> - goto free_range;
> - }
> - }
> -
> - if (!meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
> - page = NULL;
> - goto free_range;
> - }
> -
> - /* Minimise pfn page lookups and scheduler checks */
> - if (page && (pfn & (pageblock_nr_pages - 1)) != 0) {
> - page++;
> - } else {
> - nr_pages += nr_to_free;
> - deferred_free_range(free_base_page,
> - free_base_pfn, nr_to_free);
> - free_base_page = NULL;
> - free_base_pfn = nr_to_free = 0;
> -
> - page = pfn_to_page(pfn);
> - cond_resched();
> - }
> -
> - if (page->flags) {
> - VM_BUG_ON(page_zone(page) != zone);
> - goto free_range;
> - }
> -
> - __init_single_page(page, pfn, zid, nid);
> - if (!free_base_page) {
> - free_base_page = page;
> - free_base_pfn = pfn;
> - nr_to_free = 0;
> - }
> - nr_to_free++;
> -
> - /* Where possible, batch up pages for a single free */
> - continue;
> -free_range:
> - /* Free the current block of pages to allocator */
> - nr_pages += nr_to_free;
> - deferred_free_range(free_base_page, free_base_pfn,
> - nr_to_free);
> - free_base_page = NULL;
> - free_base_pfn = nr_to_free = 0;
> - }
> - /* Free the last block of pages to allocator */
> - nr_pages += nr_to_free;
> - deferred_free_range(free_base_page, free_base_pfn, nr_to_free);
> -
> - first_init_pfn = max(end_pfn, first_init_pfn);
> + 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);
> }
>
> /* Sanity check that the next zone really is unpopulated */
> --
> 2.14.2

--
Michal Hocko
SUSE Labs

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