Messages in this thread | | | Subject | Re: [PATCH 5/7] mm: move zone iterator outside of deferred_init_maxorder() | From | Alexander Duyck <> | Date | Thu, 30 Apr 2020 14:43:28 -0700 |
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On 4/30/2020 1:11 PM, Daniel Jordan wrote: > padata will soon divide up pfn ranges between threads when parallelizing > deferred init, and deferred_init_maxorder() complicates that by using an > opaque index in addition to start and end pfns. Move the index outside > the function to make splitting the job easier, and simplify the code > while at it. > > deferred_init_maxorder() now always iterates within a single pfn range > instead of potentially multiple ranges, and advances start_pfn to the > end of that range instead of the max-order block so partial pfn ranges > in the block aren't skipped in a later iteration. The section alignment > check in deferred_grow_zone() is removed as well since this alignment is > no longer guaranteed. It's not clear what value the alignment provided > originally. > > Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
So part of the reason for splitting it up along section aligned boundaries was because we already had an existing functionality in deferred_grow_zone that was going in and pulling out a section aligned chunk and processing it to prepare enough memory for other threads to keep running. I suspect that the section alignment was done because normally I believe that is also the alignment for memory onlining.
With this already breaking things up over multiple threads how does this work with deferred_grow_zone? Which thread is it trying to allocate from if it needs to allocate some memory for itself?
Also what is to prevent a worker from stop deferred_grow_zone from bailing out in the middle of a max order page block if there is a hole in the middle of the block?
> --- > mm/page_alloc.c | 88 +++++++++++++++---------------------------------- > 1 file changed, 27 insertions(+), 61 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 68669d3a5a665..990514d8f0d94 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1708,55 +1708,23 @@ deferred_init_mem_pfn_range_in_zone(u64 *i, struct zone *zone, > } > > /* > - * Initialize and free pages. We do it in two loops: first we initialize > - * struct page, then free to buddy allocator, because while we are > - * freeing pages we can access pages that are ahead (computing buddy > - * page in __free_one_page()). > - * > - * In order to try and keep some memory in the cache we have the loop > - * broken along max page order boundaries. This way we will not cause > - * any issues with the buddy page computation. > + * Initialize the struct pages and then free them to the buddy allocator at > + * most a max order block at a time because while we are freeing pages we can > + * access pages that are ahead (computing buddy page in __free_one_page()). > + * It's also cache friendly. > */ > static unsigned long __init > -deferred_init_maxorder(u64 *i, struct zone *zone, unsigned long *start_pfn, > - unsigned long *end_pfn) > +deferred_init_maxorder(struct zone *zone, unsigned long *start_pfn, > + unsigned long end_pfn) > { > - unsigned long mo_pfn = ALIGN(*start_pfn + 1, MAX_ORDER_NR_PAGES); > - unsigned long spfn = *start_pfn, epfn = *end_pfn; > - unsigned long nr_pages = 0; > - u64 j = *i; > - > - /* First we loop through and initialize the page values */ > - for_each_free_mem_pfn_range_in_zone_from(j, zone, start_pfn, end_pfn) { > - unsigned long t; > - > - if (mo_pfn <= *start_pfn) > - break; > - > - t = min(mo_pfn, *end_pfn); > - nr_pages += deferred_init_pages(zone, *start_pfn, t); > - > - if (mo_pfn < *end_pfn) { > - *start_pfn = mo_pfn; > - break; > - } > - } > - > - /* Reset values and now loop through freeing pages as needed */ > - swap(j, *i); > - > - for_each_free_mem_pfn_range_in_zone_from(j, zone, &spfn, &epfn) { > - unsigned long t; > - > - if (mo_pfn <= spfn) > - break; > + unsigned long nr_pages, pfn; > > - t = min(mo_pfn, epfn); > - deferred_free_pages(spfn, t); > + pfn = ALIGN(*start_pfn + 1, MAX_ORDER_NR_PAGES); > + pfn = min(pfn, end_pfn); > > - if (mo_pfn <= epfn) > - break; > - } > + nr_pages = deferred_init_pages(zone, *start_pfn, pfn); > + deferred_free_pages(*start_pfn, pfn); > + *start_pfn = pfn; > > return nr_pages; > } > @@ -1814,9 +1782,11 @@ static int __init deferred_init_memmap(void *data) > * that we can avoid introducing any issues with the buddy > * allocator. > */ > - while (spfn < epfn) { > - nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn); > - cond_resched(); > + for_each_free_mem_pfn_range_in_zone_from(i, zone, &spfn, &epfn) { > + while (spfn < epfn) { > + nr_pages += deferred_init_maxorder(zone, &spfn, epfn); > + cond_resched(); > + } > } > zone_empty: > /* Sanity check that the next zone really is unpopulated */ > @@ -1883,22 +1853,18 @@ deferred_grow_zone(struct zone *zone, unsigned int order) > * that we can avoid introducing any issues with the buddy > * allocator. > */ > - while (spfn < epfn) { > - /* update our first deferred PFN for this section */ > - first_deferred_pfn = spfn; > - > - nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn); > - touch_nmi_watchdog(); > - > - /* We should only stop along section boundaries */ > - if ((first_deferred_pfn ^ spfn) < PAGES_PER_SECTION) > - continue; > - > - /* If our quota has been met we can stop here */ > - if (nr_pages >= nr_pages_needed) > - break; > + for_each_free_mem_pfn_range_in_zone_from(i, zone, &spfn, &epfn) { > + while (spfn < epfn) { > + nr_pages += deferred_init_maxorder(zone, &spfn, epfn); > + touch_nmi_watchdog(); > + > + /* If our quota has been met we can stop here */ > + if (nr_pages >= nr_pages_needed) > + goto out; > + } > } > > +out: > pgdat->first_deferred_pfn = spfn; > pgdat_resize_unlock(pgdat, &flags); > >
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