On Sat, Jun 19, 2021 at 12:45 AM Huang, Ying <ying.huang@xxxxxxxxx> wrote: > > Zi Yan <ziy@xxxxxxxxxx> writes: > > > On 18 Jun 2021, at 2:15, Huang Ying 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> > >> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> > >> Cc: Michal Hocko <mhocko@xxxxxxxx> > >> Cc: Wei Xu <weixugc@xxxxxxxxxx> > >> Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> > >> Cc: David Rientjes <rientjes@xxxxxxxxxx> > >> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > >> Cc: osalvador <osalvador@xxxxxxx> > >> > >> -- > >> changes from 20210122: > >> * move from GFP_HIGHUSER -> GFP_HIGHUSER_MOVABLE (Ying) > >> > >> 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. > >> changes from 20210302: > >> * Use __GFP_THISNODE and revise the comment explaining the > >> GFP mask constructionn > >> --- > >> include/linux/migrate.h | 9 ++++ > >> include/trace/events/migrate.h | 3 +- > >> mm/vmscan.c | 83 ++++++++++++++++++++++++++++++++++ > >> 3 files changed, 94 insertions(+), 1 deletion(-) > >> > >> diff --git a/include/linux/migrate.h b/include/linux/migrate.h > >> index 4a49bb358787..42952cbe452b 100644 > >> --- a/include/linux/migrate.h > >> +++ b/include/linux/migrate.h > >> @@ -28,6 +28,7 @@ enum migrate_reason { > >> MR_NUMA_MISPLACED, > >> MR_CONTIG_RANGE, > >> MR_LONGTERM_PIN, > >> + MR_DEMOTION, > >> MR_TYPES > >> }; > >> > >> @@ -191,6 +192,14 @@ 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 --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h > >> index 9fb2a3bbcdfb..779f3fad9ecd 100644 > >> --- a/include/trace/events/migrate.h > >> +++ b/include/trace/events/migrate.h > >> @@ -21,7 +21,8 @@ > >> EM( MR_MEMPOLICY_MBIND, "mempolicy_mbind") \ > >> EM( MR_NUMA_MISPLACED, "numa_misplaced") \ > >> EM( MR_CONTIG_RANGE, "contig_range") \ > >> - EMe(MR_LONGTERM_PIN, "longterm_pin") > >> + EM( MR_LONGTERM_PIN, "longterm_pin") \ > >> + EMe(MR_DEMOTION, "demotion") > >> > >> /* > >> * First define the enums in the above macros to be exported to userspace > >> diff --git a/mm/vmscan.c b/mm/vmscan.c > >> index 5199b9696bab..ddda32031f0c 100644 > >> --- a/mm/vmscan.c > >> +++ b/mm/vmscan.c > >> @@ -41,6 +41,7 @@ > >> #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> > >> @@ -1231,6 +1232,23 @@ static enum page_references page_check_references(struct page *page, > >> 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) > >> @@ -1261,6 +1279,47 @@ static void page_check_dirty_writeback(struct page *page, > >> 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 = { > >> + /* > >> + * Allocate from 'node', or fail the quickly and quietly. > >> + * When this happens, 'page; will likely just be discarded > >> + * instead of migrated. > >> + */ > >> + .gfp_mask = (GFP_HIGHUSER_MOVABLE & ~__GFP_RECLAIM) | > >> + __GFP_THISNODE | __GFP_NOWARN | > >> + __GFP_NOMEMALLOC | GFP_NOWAIT, > >> + .nid = node > >> + }; > >> + > >> + return alloc_migration_target(page, (unsigned long)&mtc); > >> +} > >> + > >> +/* > >> + * 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 > >> */ > >> @@ -1272,12 +1331,15 @@ static unsigned int shrink_page_list(struct list_head *page_list, > >> { > >> 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; > >> @@ -1426,6 +1488,16 @@ static unsigned int shrink_page_list(struct list_head *page_list, > >> ; /* try to reclaim the page below */ > >> } > >> > >> + /* > >> + * 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. > >> @@ -1676,6 +1748,17 @@ static unsigned int shrink_page_list(struct list_head *page_list, > >> 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 @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]; > >> > >> -- > >> 2.30.2 > > > > shrink_page_list() is also used by reclaim_pages(), which is called by > > madvise(MADV_PAGEOUT). This patch changes the semantics of madvise(MADV_PAGEOUT) > > from “reclaim a given range of pages” to migrate the given pages to lower > > tier memory or reclaim them if the migration fails. You might want to check > > the caller of shrink_page_list() to avoid changing madvise(MADV_PAGEOUT) > > semantics. > > Thanks for pointing this out! > > Literally, PAGEOUT means writing the page to the disk instead of > migrating pages to the lower tier. So it seems reasonable to make it > keep the original behavior instead of demoting even if in the tiered > memory system. > > If nobody objects, I will change this in the next version. I don't have a strong opinion on this. But I just thought why not let PAGEOUT do demotion if tier'ed memory is available and the "migration in lieu of discard" behavior is opt'ed in by a knob and we keep the consistency between passive reclaim and proactive reclaim. > > Best Regards, > Huang, Ying >
