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SubjectRe: [PATCH -V9 4/9] mm/migrate: demote pages during reclaim
Date
Wei Xu <weixugc@google.com> writes:

> On Fri, Jun 25, 2021 at 12:33 AM Huang Ying <ying.huang@intel.com> wrote:
>>
>> From: Dave Hansen <dave.hansen@linux.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@linux.intel.com>
>> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
>> Reviewed-by: Yang Shi <shy828301@gmail.com>
>> Reviewed-by: Wei Xu <weixugc@google.com>
>> Reviewed-by: Oscar Salvador <osalvador@suse.de>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Zi Yan <ziy@nvidia.com>
>> Cc: David Rientjes <rientjes@google.com>
>> Cc: Dan Williams <dan.j.williams@intel.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.

Sounds good to me! Thanks! Will change this in the next version.

Best Regards,
Huang, Ying

>> + 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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