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.

[akpm@linux-foundation.org: fix spello in comment]
Link: http://lkml.kernel.org/r/20171107150446.32055-2-pasha.tatashin@oracle.com
Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Acked-by: Michal Hocko <mhocko@suse.com>
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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 76 insertions, 70 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 76c9688b6a0a..a73cffe287a5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1457,92 +1457,87 @@ static inline void __init pgdat_init_report_one_done(void)
 }
 
 /*
- * 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 or 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(void *data)
         }
         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 */