Yang Shi <shy828301@xxxxxxxxx> writes: > 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. I thought about that too. Considering the kernel API naming, is it better to define MADV_PAGEOUT as writing to disk, and MADV_COLD as demoting to the lower tier if enabled. Best Regards, Huang, Ying
