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Message-ID: <CAAPL-u_wnxWTedy7hZe0mtkHXo2jWihnZ_z+MD_XvLHQ+84w2w@mail.gmail.com>
Date: Fri, 25 Jun 2021 17:21:40 -0700
From: Wei Xu <weixugc@...gle.com>
To: Huang Ying <ying.huang@...el.com>
Cc: Linux MM <linux-mm@...ck.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Yang Shi <shy828301@...il.com>,
Oscar Salvador <osalvador@...e.de>,
Michal Hocko <mhocko@...e.com>, Zi Yan <ziy@...dia.com>,
David Rientjes <rientjes@...gle.com>,
Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH -V9 4/9] mm/migrate: demote pages during reclaim
On Fri, Jun 25, 2021 at 12:33 AM Huang Ying <ying.huang@...el.com> wrote:
>
> From: Dave Hansen <dave.hansen@...ux.intel.com>
>
> This is mostly derived from a patch from Yang Shi:
>
> https://lore.kernel.org/linux-mm/1560468577-101178-10-git-send-email-yang.shi@linux.alibaba.com/
>
> 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 page is dirty.
>
> A second pass through shrink_page_list() will be made if any demotions
> fail. This essentially 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.
>
> For some cases, for example, MADV_PAGEOUT, the pages are always
> discarded instead of demoted to follow the kernel API definition.
> Because MADV_PAGEOUT is defined as freeing specified pages regardless
> in which tier they are.
>
> Note: This just adds the start of infrastructure for migration. It is
> actually disabled next to the FIXME in migrate_demote_page_ok().
>
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Reviewed-by: Yang Shi <shy828301@...il.com>
> Reviewed-by: Wei Xu <weixugc@...gle.com>
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
>
> --
> changes from 20210618:
> * Fix some typos in comments and patch description.
> * Fix MADV_PAGEOUT behavior per Zi's comments.
>
> 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 | 93 ++++++++++++++++++++++++++++++++++
> 3 files changed, 104 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 166dc1fe4eee..d678e02a27ff 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..badaf3d4360d 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>
> @@ -118,6 +119,9 @@ struct scan_control {
> /* The file pages on the current node are dangerously low */
> unsigned int file_is_tiny:1;
>
> + /* Always discard instead of demoting to lower tier memory */
> + unsigned int no_demotion:1;
> +
> /* Allocation order */
> s8 order;
>
> @@ -1231,6 +1235,27 @@ static enum page_references page_check_references(struct page *page,
> return PAGEREF_RECLAIM;
> }
>
> +static bool migrate_demote_page_ok(struct page *page,
> + struct scan_control *sc)
> +{
> + int next_nid;
> +
> + VM_BUG_ON_PAGE(!PageLocked(page), page);
> + VM_BUG_ON_PAGE(PageHuge(page), page);
> + VM_BUG_ON_PAGE(PageLRU(page), page);
> +
> + if (sc->no_demotion)
> + return false;
> + next_nid = next_demotion_node(page_to_nid(page));
> + if (next_nid == NUMA_NO_NODE)
> + return false;
The above sc and node checks are not specific to the page. They can
be moved into shrink_page_list() to set do_demote_pass accordingly.
We then don't need to repeat these checks for every page.
> + 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 +1286,49 @@ 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 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)
> +{
> + int target_nid = next_demotion_node(pgdat->node_id);
> + unsigned int nr_succeeded;
> + int err;
> +
> + if (list_empty(demote_pages))
> + return 0;
> +
> + if (target_nid == NUMA_NO_NODE)
> + 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 +1340,15 @@ 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 +1497,16 @@ 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, sc)) {
> + 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 +1757,17 @@ 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);
> + /* 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];
>
> @@ -2312,6 +2404,7 @@ unsigned long reclaim_pages(struct list_head *page_list)
> .may_writepage = 1,
> .may_unmap = 1,
> .may_swap = 1,
> + .no_demotion = 1,
> };
>
> while (!list_empty(page_list)) {
> --
> 2.30.2
>
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