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mm: split deferred_init_range into initializing and freeing parts
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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>
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Pavel Tatashin authored and Linus Torvalds committed Feb 1, 2018
1 parent 9092c71 commit 80b1f41
Showing 1 changed file with 76 additions and 70 deletions.
146 changes: 76 additions & 70 deletions mm/page_alloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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 */
Expand Down Expand Up @@ -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 */
Expand Down

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