On Tue 21-11-17 15:44:51, Andrew Morton wrote: > ------------------------------------------------------ > From: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> > Subject: 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. I thought I have acked this one. Let me dig that out. ... Ohh, here it is https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1528267.html > > Link: http://lkml.kernel.org/r/20171107150446.32055-2-pasha.tatashin@xxxxxxxxxx > Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Cc: Steven Sistare <steven.sistare@xxxxxxxxxx> > Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> > --- > > mm/page_alloc.c | 146 +++++++++++++++++++++++----------------------- > 1 file changed, 76 insertions(+), 70 deletions(-) > > diff -puN mm/page_alloc.c~mm-split-deferred_init_range-into-initializing-and-freeing-parts mm/page_alloc.c > --- a/mm/page_alloc.c~mm-split-deferred_init_range-into-initializing-and-freeing-parts > +++ a/mm/page_alloc.c > @@ -1457,92 +1457,87 @@ static inline void __init pgdat_init_rep > } > > /* > - * 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(v > } > 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 */ > _ > > Patches currently in -mm which might be from pasha.tatashin@xxxxxxxxxx are > > mm-relax-deferred-struct-page-requirements.patch > mm-split-deferred_init_range-into-initializing-and-freeing-parts.patch > sparc64-ng4-memset-32-bits-overflow.patch -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
