On Mon, Jan 25, 2021 at 4:41 PM Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote: > > > From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > > This is mostly derived from a patch from Yang Shi: > > https://lore.kernel.org/linux-mm/1560468577-101178-10-git-send-email-yang.shi@xxxxxxxxxxxxxxxxx/ > > Add code to the reclaim path (shrink_page_list()) to "demote" data > to another NUMA node instead of discarding the data. This always > avoids the cost of I/O needed to read the page back in and sometimes > avoids the writeout cost when the pagee is dirty. > > A second pass through shrink_page_list() will be made if any demotions > fail. This essentally falls back to normal reclaim behavior in the > case that demotions fail. Previous versions of this patch may have > simply failed to reclaim pages which were eligible for demotion but > were unable to be demoted in practice. > > Note: This just adds the start of infratructure for migration. It is > actually disabled next to the FIXME in migrate_demote_page_ok(). > > Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> > Cc: David Rientjes <rientjes@xxxxxxxxxx> > Cc: Huang Ying <ying.huang@xxxxxxxxx> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > Cc: osalvador <osalvador@xxxxxxx> > > -- > > changes from 202010: > * add MR_NUMA_MISPLACED to trace MIGRATE_REASON define > * make migrate_demote_page_ok() static, remove 'sc' arg until > later patch > * remove unnecessary alloc_demote_page() hugetlb warning > * Simplify alloc_demote_page() gfp mask. Depend on > __GFP_NORETRY to make it lightweight instead of fancier > stuff like leaving out __GFP_IO/FS. > * Allocate migration page with alloc_migration_target() > instead of allocating directly. > changes from 20200730: > * Add another pass through shrink_page_list() when demotion > fails. > --- > > b/include/linux/migrate.h | 9 ++++ > b/include/trace/events/migrate.h | 3 - > b/mm/vmscan.c | 81 +++++++++++++++++++++++++++++++++++++++ > 3 files changed, 92 insertions(+), 1 deletion(-) > > diff -puN include/linux/migrate.h~demote-with-migrate_pages include/linux/migrate.h > --- a/include/linux/migrate.h~demote-with-migrate_pages 2021-01-25 16:23:14.591866696 -0800 > +++ b/include/linux/migrate.h 2021-01-25 16:23:14.599866696 -0800 > @@ -27,6 +27,7 @@ enum migrate_reason { > MR_MEMPOLICY_MBIND, > MR_NUMA_MISPLACED, > MR_CONTIG_RANGE, > + MR_DEMOTION, > MR_TYPES > }; > > @@ -196,6 +197,14 @@ struct migrate_vma { > int migrate_vma_setup(struct migrate_vma *args); > void migrate_vma_pages(struct migrate_vma *migrate); > void migrate_vma_finalize(struct migrate_vma *migrate); > +int next_demotion_node(int node); > + > +#else /* CONFIG_MIGRATION disabled: */ > + > +static inline int next_demotion_node(int node) > +{ > + return NUMA_NO_NODE; > +} > > #endif /* CONFIG_MIGRATION */ > > diff -puN include/trace/events/migrate.h~demote-with-migrate_pages include/trace/events/migrate.h > --- a/include/trace/events/migrate.h~demote-with-migrate_pages 2021-01-25 16:23:14.593866696 -0800 > +++ b/include/trace/events/migrate.h 2021-01-25 16:23:14.599866696 -0800 > @@ -20,7 +20,8 @@ > EM( MR_SYSCALL, "syscall_or_cpuset") \ > EM( MR_MEMPOLICY_MBIND, "mempolicy_mbind") \ > EM( MR_NUMA_MISPLACED, "numa_misplaced") \ > - EMe(MR_CONTIG_RANGE, "contig_range") > + EM( MR_CONTIG_RANGE, "contig_range") \ > + EMe(MR_DEMOTION, "demotion") > > /* > * First define the enums in the above macros to be exported to userspace > diff -puN mm/vmscan.c~demote-with-migrate_pages mm/vmscan.c > --- a/mm/vmscan.c~demote-with-migrate_pages 2021-01-25 16:23:14.595866696 -0800 > +++ b/mm/vmscan.c 2021-01-25 16:23:14.601866696 -0800 > @@ -43,6 +43,7 @@ > #include <linux/kthread.h> > #include <linux/freezer.h> > #include <linux/memcontrol.h> > +#include <linux/migrate.h> > #include <linux/delayacct.h> > #include <linux/sysctl.h> > #include <linux/oom.h> > @@ -1036,6 +1037,24 @@ static enum page_references page_check_r > return PAGEREF_RECLAIM; > } > > +static bool migrate_demote_page_ok(struct page *page) > +{ > + int next_nid = next_demotion_node(page_to_nid(page)); > + > + VM_BUG_ON_PAGE(!PageLocked(page), page); > + VM_BUG_ON_PAGE(PageHuge(page), page); > + VM_BUG_ON_PAGE(PageLRU(page), page); > + > + if (next_nid == NUMA_NO_NODE) > + return false; > + if (PageTransHuge(page) && !thp_migration_supported()) > + return false; > + > + // FIXME: actually enable this later in the series > + return false; > +} > + > + > /* Check if a page is dirty or under writeback */ > static void page_check_dirty_writeback(struct page *page, > bool *dirty, bool *writeback) > @@ -1066,6 +1085,44 @@ static void page_check_dirty_writeback(s > mapping->a_ops->is_dirty_writeback(page, dirty, writeback); > } > > +static struct page *alloc_demote_page(struct page *page, unsigned long node) > +{ > + struct migration_target_control mtc = { > + /* > + * Fail quickly and quietly. Page will likely > + * just be discarded instead of migrated. > + */ > + .gfp_mask = GFP_HIGHUSER | __GFP_NORETRY | __GFP_NOWARN, > + .nid = node > + }; > + > + return alloc_migration_target(page, (unsigned long)&mtc); Other than the gfp flag question raised by Oscar, I'm wondering how we guarantee the demotion allocation happens on the designated node. In the previous version __GFP_THISNODE is set to guarantee this. In this version you switched to use alloc_migration_target() API but without having nodemask or __GFP_THISNODE. If nodemask is NULL the allocation may fall back to an unexpected node. And GFP_HIGHUSER does respect cpuset, so if the demotion target node is excluded by the cpuset which the task belongs to, the migration would fail. This might be a way to respect cpuset, but it should just work for direct reclaimer. So, is this change really expected? > +} > + > +/* > + * Take pages on @demote_list and attempt to demote them to > + * another node. Pages which are not demoted are left on > + * @demote_pages. > + */ > +static unsigned int demote_page_list(struct list_head *demote_pages, > + struct pglist_data *pgdat, > + struct scan_control *sc) > +{ > + int target_nid = next_demotion_node(pgdat->node_id); > + unsigned int nr_succeeded = 0; > + int err; > + > + if (list_empty(demote_pages)) > + return 0; > + > + /* Demotion ignores all cpuset and mempolicy settings */ > + err = migrate_pages(demote_pages, alloc_demote_page, NULL, > + target_nid, MIGRATE_ASYNC, MR_DEMOTION, > + &nr_succeeded); > + > + return nr_succeeded; > +} > + > /* > * shrink_page_list() returns the number of reclaimed pages > */ > @@ -1078,12 +1135,15 @@ static unsigned int shrink_page_list(str > { > LIST_HEAD(ret_pages); > LIST_HEAD(free_pages); > + LIST_HEAD(demote_pages); > unsigned int nr_reclaimed = 0; > unsigned int pgactivate = 0; > + bool do_demote_pass = true; > > memset(stat, 0, sizeof(*stat)); > cond_resched(); > > +retry: > while (!list_empty(page_list)) { > struct address_space *mapping; > struct page *page; > @@ -1233,6 +1293,16 @@ static unsigned int shrink_page_list(str > } > > /* > + * Before reclaiming the page, try to relocate > + * its contents to another node. > + */ > + if (do_demote_pass && migrate_demote_page_ok(page)) { > + list_add(&page->lru, &demote_pages); > + unlock_page(page); > + continue; > + } > + > + /* > * Anonymous process memory has backing store? > * Try to allocate it some swap space here. > * Lazyfree page could be freed directly > @@ -1479,6 +1549,17 @@ keep: > list_add(&page->lru, &ret_pages); > VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page); > } > + /* 'page_list' is always empty here */ > + > + /* Migrate pages selected for demotion */ > + nr_reclaimed += demote_page_list(&demote_pages, pgdat, sc); > + /* Pages that could not be demoted are still in @demote_pages */ > + if (!list_empty(&demote_pages)) { > + /* Pages which failed to demoted go back on on @page_list for retry: */ > + list_splice_init(&demote_pages, page_list); > + do_demote_pass = false; > + goto retry; > + } > > pgactivate = stat->nr_activate[0] + stat->nr_activate[1]; > > _ >
