Messages in this thread | | | Date | Mon, 6 Jun 2022 13:32:59 +0530 | Subject | Re: [RFC PATCH v4 7/7] mm/demotion: Demote pages according to allocation fallback order | From | Aneesh Kumar K V <> |
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On 6/6/22 1:12 PM, Ying Huang wrote: > On Mon, 2022-06-06 at 11:51 +0530, Aneesh Kumar K.V wrote: >> Ying Huang <ying.huang@intel.com> writes: >> >> ..... >> >>>>>> >>>>>>> https://lore.kernel.org/lkml/69f2d063a15f8c4afb4688af7b7890f32af55391.camel@intel.com/ >>>>>>> >>>>>>> That is, something like below, >>>>>>> >>>>>>> static struct page *alloc_demote_page(struct page *page, unsigned long node) >>>>>>> { >>>>>>> struct page *page; >>>>>>> nodemask_t allowed_mask; >>>>>>> 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 >>>>>>> }; >>>>>>> >>>>>>> page = alloc_migration_target(page, (unsigned long)&mtc); >>>>>>> if (page) >>>>>>> return page; >>>>>>> >>>>>>> mtc.gfp_mask &= ~__GFP_THISNODE; >>>>>>> mtc.nmask = &allowed_mask; >>>>>>> >>>>>>> return alloc_migration_target(page, (unsigned long)&mtc); >>>>>>> } >>>>>> >>>>>> I skipped doing this in v5 because I was not sure this is really what we >>>>>> want. >>>>> >>>>> I think so. And this is the original behavior. We should keep the >>>>> original behavior as much as possible, then make changes if necessary. >>>>> >>>> >>>> That is the reason I split the new page allocation as a separate patch. >>>> Previous discussion on this topic didn't conclude on whether we really >>>> need to do the above or not >>>> https://lore.kernel.org/lkml/CAAPL-u9endrWf_aOnPENDPdvT-2-YhCAeJ7ONGckGnXErTLOfQ@mail.gmail.com/ >>> >>> Please check the later email in the thread you referenced. Both Wei and >>> me agree that the use case needs to be supported. We just didn't reach >>> concensus about how to implement it. If you think Wei's solution is >>> better (referenced as below), you can try to do that too. Although I >>> think my proposed implementation is much simpler. >> >> How about the below details >> >> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h >> index 79bd8d26feb2..cd6e71f702ad 100644 >> --- a/include/linux/memory-tiers.h >> +++ b/include/linux/memory-tiers.h >> @@ -21,6 +21,7 @@ void node_remove_from_memory_tier(int node); >> int node_get_memory_tier_id(int node); >> int node_set_memory_tier(int node, int tier); >> int node_reset_memory_tier(int node, int tier); >> +void node_get_allowed_targets(int node, nodemask_t *targets); >> #else >> #define numa_demotion_enabled false >> static inline int next_demotion_node(int node) >> @@ -28,6 +29,10 @@ static inline int next_demotion_node(int node) >> return NUMA_NO_NODE; >> } >> >> >> >> >> +static inline void node_get_allowed_targets(int node, nodemask_t *targets) >> +{ >> + *targets = NODE_MASK_NONE; >> +} >> #endif /* CONFIG_TIERED_MEMORY */ >> >> >> >> >> #endif >> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c >> index b4e72b672d4d..592d939ec28d 100644 >> --- a/mm/memory-tiers.c >> +++ b/mm/memory-tiers.c >> @@ -18,6 +18,7 @@ struct memory_tier { >> >> >> >> >> struct demotion_nodes { >> nodemask_t preferred; >> + nodemask_t allowed; >> }; >> >> >> >> >> #define to_memory_tier(device) container_of(device, struct memory_tier, dev) >> @@ -378,6 +379,25 @@ int node_set_memory_tier(int node, int tier) >> } >> EXPORT_SYMBOL_GPL(node_set_memory_tier); >> >> >> >> >> +void node_get_allowed_targets(int node, nodemask_t *targets) >> +{ >> + /* >> + * node_demotion[] is updated without excluding this >> + * function from running. >> + * >> + * If any node is moving to lower tiers then modifications >> + * in node_demotion[] are still valid for this node, if any >> + * node is moving to higher tier then moving node may be >> + * used once for demotion which should be ok so rcu should >> + * be enough here. >> + */ >> + rcu_read_lock(); >> + >> + *targets = node_demotion[node].allowed; >> + >> + rcu_read_unlock(); >> +} >> + >> /** >> * next_demotion_node() - Get the next node in the demotion path >> * @node: The starting node to lookup the next node >> @@ -437,8 +457,10 @@ static void __disable_all_migrate_targets(void) >> { >> int node; >> >> >> >> >> - for_each_node_mask(node, node_states[N_MEMORY]) >> + for_each_node_mask(node, node_states[N_MEMORY]) { >> node_demotion[node].preferred = NODE_MASK_NONE; >> + node_demotion[node].allowed = NODE_MASK_NONE; >> + } >> } >> >> >> >> >> static void disable_all_migrate_targets(void) >> @@ -465,7 +487,7 @@ static void establish_migration_targets(void) >> struct demotion_nodes *nd; >> int target = NUMA_NO_NODE, node; >> int distance, best_distance; >> - nodemask_t used; >> + nodemask_t used, allowed = NODE_MASK_NONE; >> >> >> >> >> if (!node_demotion) >> return; >> @@ -511,6 +533,29 @@ static void establish_migration_targets(void) >> } >> } while (1); >> } >> + /* >> + * Now build the allowed mask for each node collecting node mask from >> + * all memory tier below it. This allows us to fallback demotion page >> + * allocation to a set of nodes that is closer the above selected >> + * perferred node. >> + */ >> + list_for_each_entry(memtier, &memory_tiers, list) >> + nodes_or(allowed, allowed, memtier->nodelist); >> + /* >> + * Removes nodes not yet in N_MEMORY. >> + */ >> + nodes_and(allowed, node_states[N_MEMORY], allowed); >> + >> + list_for_each_entry(memtier, &memory_tiers, list) { >> + /* >> + * Keep removing current tier from allowed nodes, >> + * This will remove all nodes in current and above >> + * memory tier from the allowed mask. >> + */ >> + nodes_andnot(allowed, allowed, memtier->nodelist); >> + for_each_node_mask(node, memtier->nodelist) >> + node_demotion[node].allowed = allowed; >> + } >> } >> >> >> >> >> /* >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 3a8f78277f99..b0792d838efb 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -1460,19 +1460,32 @@ static void folio_check_dirty_writeback(struct folio *folio, >> mapping->a_ops->is_dirty_writeback(folio, dirty, writeback); >> } >> >> >> >> >> -static struct page *alloc_demote_page(struct page *page, unsigned long node) >> +static struct page *alloc_demote_page(struct page *page, unsigned long private) >> { >> - 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 >> - }; >> + struct page *target_page; >> + nodemask_t *allowed_mask; >> + struct migration_target_control *mtc; >> + >> + mtc = (struct migration_target_control *)private; >> + >> + allowed_mask = mtc->nmask; >> + /* >> + * make sure we allocate from the target node first also trying to >> + * reclaim pages from the target node via kswapd if we are low on >> + * free memory on target node. If we don't do this and if we have low >> + * free memory on the target memtier, we would start allocating pages >> + * from higher memory tiers without even forcing a demotion of cold >> + * pages from the target memtier. This can result in the kernel placing >> + * hotpages in higher memory tiers. >> + */ >> + mtc->nmask = NULL; >> + mtc->gfp_mask |= __GFP_THISNODE; >> + target_page = alloc_migration_target(page, (unsigned long)&mtc); >> + if (target_page) >> + return target_page; >> + >> + mtc->gfp_mask &= ~__GFP_THISNODE; >> + mtc->nmask = allowed_mask; >> >> >> >> >> return alloc_migration_target(page, (unsigned long)&mtc); >> } >> @@ -1487,6 +1500,19 @@ static unsigned int demote_page_list(struct list_head *demote_pages, >> { >> int target_nid = next_demotion_node(pgdat->node_id); >> unsigned int nr_succeeded; >> + nodemask_t allowed_mask; >> + >> + 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_NOWARN | >> + __GFP_NOMEMALLOC | GFP_NOWAIT, >> + .nid = target_nid, >> + .nmask = &allowed_mask >> + }; >> >> >> >> >> if (list_empty(demote_pages)) >> return 0; >> @@ -1494,10 +1520,12 @@ static unsigned int demote_page_list(struct list_head *demote_pages, >> if (target_nid == NUMA_NO_NODE) >> return 0; >> >> >> >> >> + node_get_allowed_targets(pgdat->node_id, &allowed_mask); >> + >> /* Demotion ignores all cpuset and mempolicy settings */ >> migrate_pages(demote_pages, alloc_demote_page, NULL, >> - target_nid, MIGRATE_ASYNC, MR_DEMOTION, >> - &nr_succeeded); >> + (unsigned long)&mtc, MIGRATE_ASYNC, MR_DEMOTION, >> + &nr_succeeded); > > Firstly, it addressed my requirement, Thanks! And, I'd prefer to put > mtc definition in alloc_demote_page(). Because that makes all page > allocation logic in one function. Thus the readability of code is > better.
The challenge is in allowed_mask computation. That is based on the src_node and not target_node.
-aneesh
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