From 80b1f41c0957a9da3bab4fb9ae76dc886753a59b Mon Sep 17 00:00:00 2001 From: Pavel Tatashin Date: Wed, 31 Jan 2018 16:16:30 -0800 Subject: [PATCH] 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 Acked-by: Michal Hocko Cc: Steven Sistare Cc: Daniel Jordan Cc: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 76c9688..a73cffe 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 */ -- 2.7.4