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Date: Tue, 7 Nov 2017 10:04:46 -0500
From: Pavel Tatashin <pasha.tatashin@...cle.com>
To: steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
akpm@...ux-foundation.org, mgorman@...hsingularity.net,
mhocko@...e.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1 1/1] 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.
Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
---
mm/page_alloc.c | 146 +++++++++++++++++++++++++++++---------------------------
1 file changed, 76 insertions(+), 70 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 536431bf0f0c..d9f1e7159af8 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 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(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 */
--
2.15.0
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