Joshua Hahn <joshua.hahnjy@xxxxxxxxx> writes: > On machines with multiple memory nodes, interleaving page allocations > across nodes allows for better utilization of each node's bandwidth. > Previous work by Gregory Price [1] introduced weighted interleave, which > allowed for pages to be allocated across NUMA nodes according to > user-set ratios. > > Ideally, these weights should be proportional to their bandwidth, so > that under bandwidth pressure, each node uses its maximal efficient > bandwidth and prevents latency from increasing exponentially. > > At the same time, we want these weights to be as small as possible. > Having ratios that involve large co-prime numbers like 7639:1345:7 leads > to awkward and inefficient allocations, since the node with weight 7 > will remain mostly unused (and despite being proportional to bandwidth, > will not aid in relieving the bandwidth pressure in the other two nodes). > > This patch introduces an auto-configuration mode for the interleave > weights that aims to balance the two goals of setting node weights to be > proportional to their bandwidths and keeping the weight values low. > In order to perform the weight re-scaling, we use an internal > "weightiness" value (fixed to 32) that defines interleave aggression. > > In this auto configuration mode, node weights are dynamically updated > every time there is a hotplug event that introduces new bandwidth. > > Users can also enter manual mode by writing "manual" to the new "mode" > sysfs interface. When a user enters manual mode, the system stops > dynamically updating any of the node weights, even during hotplug events > that can shift the optimal weight distribution. The system also enters > manual mode any time a user sets a node's weight by hand, using the > nodeN interface introduced in [1]. On the other hand, auto mode is > only entered by explicitly writing "auto" to the mode interface. > > There is one functional change that this patch makes to the existing > weighted_interleave ABI: previously, writing 0 directly to a nodeN > interface was said to reset the weight to the system default. Before > this patch, the default for all weights were 1, which meant that writing > 0 and 1 were functionally equivalent. > > This patch introduces "real" defaults, but we have decided to move away > from letting users use 0 as a "set to default" interface. Rather, users > who want to use system defaults should use "auto" mode. This patch seems > to be the appropriate place to make this change, since we would like to > remove this usage before users begin to rely on the feature in > userspace. Moreover, users will not be losing any functionality; they > can still write 1 into a node if they want a weight of 1. Thus, we > deprecate the "write zero to reset" feature in favor of returning an > error, the same way we would return an error when the user writes any > other invalid weight to the interface. > > [1] https://lore.kernel.org/linux-mm/20240202170238.90004-1-gregory.price@xxxxxxxxxxxx/ > > Signed-off-by: Joshua Hahn <joshua.hahnjy@xxxxxxxxx> > Co-developed-by: Gregory Price <gourry@xxxxxxxxxx> > Signed-off-by: Gregory Price <gourry@xxxxxxxxxx> > --- > Changelog > v3: > - Weightiness (max_node_weight) is now fixed to 32. > - Instead, the sysfs interface now exposes a "mode" parameter, which > can either be "auto" or "manual". > - Thank you Hyeonggon and Honggyu for the feedback. > - Documentation updated to reflect new sysfs interface, explicitly > specifies that 0 is invalid. > - Thank you Gregory and Ying for the discussion on how best to > handle the 0 case. > - Re-worked nodeN sysfs store to handle auto --> manual shifts > - mempolicy_set_node_perf internally handles the auto / manual > caes differently now. bw is always updated, iw updates depend on > what mode the user is in. > - Wordsmithing comments for clarity. > - Removed RFC tag. > > v2: > - Name of the interface is changed: "max_node_weight" --> "weightiness" > - Default interleave weight table no longer exists. Rather, the > interleave weight table is initialized with the defaults, if bandwidth > information is available. > - In addition, all sections that handle iw_table have been changed > to reference iw_table if it exists, otherwise defaulting to 1. > - All instances of unsigned long are converted to uint64_t to guarantee > support for both 32-bit and 64-bit machines > - sysfs initialization cleanup > - Documentation has been rewritten to explicitly outline expected > behavior and expand on the interpretation of "weightiness". > - kzalloc replaced with kcalloc for readability > - Thank you Gregory and Hyeonggon for your review & feedback! > > ...fs-kernel-mm-mempolicy-weighted-interleave | 30 ++- > drivers/acpi/numa/hmat.c | 1 + > drivers/base/node.c | 7 + > include/linux/mempolicy.h | 4 + > mm/mempolicy.c | 212 ++++++++++++++++-- > 5 files changed, 227 insertions(+), 27 deletions(-) > > diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave > index 0b7972de04e9..d30dc29c53ff 100644 > --- a/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave > +++ b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave > @@ -20,6 +20,30 @@ Description: Weight configuration interface for nodeN > Minimum weight: 1 > Maximum weight: 255 > > - Writing an empty string or `0` will reset the weight to the > - system default. The system default may be set by the kernel > - or drivers at boot or during hotplug events. > + Writing invalid values (i.e. any values not in [1,255], > + empty string, ...) will return -EINVAL. > + > +What: /sys/kernel/mm/mempolicy/weighted_interleave/mode > +Date: January 2025 > +Contact: Linux memory management mailing list <linux-mm@xxxxxxxxx> > +Description: Auto-weighting configuration interface > + > + Configuration modes for weighted interleave. Can take one of > + two options: "manual" and "auto". Default is "auto". > + > + In auto mode, all node weights are re-calculated and overwritten > + (visible via the nodeN interfaces) whenever new bandwidth data > + is made available either during boot or hotplug events. > + > + In manual mode, node weights can only be updated by the user. > + If a node is hotplugged while the user is in manual mode, > + the node will have a default weight of 1. > + > + Modes can be changed by writing either "auto" or "manual" to the > + interface. All other strings will be ignored, and -EINVAL will > + be returned. If "auto" is written to the interface but the > + recalculation / updates fail at any point (-ENOMEM or -ENODEV) > + then the mode will remain in manual mode. > + > + Writing a new weight to a node directly via the nodeN interface > + will also automatically update the system to manual mode. IMHO, this interface is somewhat hard to be used. Users need to know which value is legal. So, this will become something like, $ cat mode auto [manual] $ echo auto > mode $ cat mode [auto] manual Unless it's possible we will add more modes in the future, this is kind of overkill for me. How about something simpler as below? $ cat auto true $ echo 0 > auto $ cat auto false > diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c > index 80a3481c0470..cc94cba112dd 100644 > --- a/drivers/acpi/numa/hmat.c > +++ b/drivers/acpi/numa/hmat.c > @@ -20,6 +20,7 @@ > #include <linux/list_sort.h> > #include <linux/memregion.h> > #include <linux/memory.h> > +#include <linux/mempolicy.h> > #include <linux/mutex.h> > #include <linux/node.h> > #include <linux/sysfs.h> > diff --git a/drivers/base/node.c b/drivers/base/node.c > index 0ea653fa3433..16e7a5a8ebe7 100644 > --- a/drivers/base/node.c > +++ b/drivers/base/node.c > @@ -7,6 +7,7 @@ > #include <linux/init.h> > #include <linux/mm.h> > #include <linux/memory.h> > +#include <linux/mempolicy.h> > #include <linux/vmstat.h> > #include <linux/notifier.h> > #include <linux/node.h> > @@ -214,6 +215,12 @@ void node_set_perf_attrs(unsigned int nid, struct access_coordinate *coord, > break; > } > } > + > + /* When setting CPU access coordinates, update mempolicy */ > + if (access == ACCESS_COORDINATE_CPU) { > + if (mempolicy_set_node_perf(nid, coord)) > + pr_info("failed to set node%d mempolicy attrs\n", nid); > + } > } > EXPORT_SYMBOL_GPL(node_set_perf_attrs); > > diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h > index ce9885e0178a..0fe96f3ab3ef 100644 > --- a/include/linux/mempolicy.h > +++ b/include/linux/mempolicy.h > @@ -11,6 +11,7 @@ > #include <linux/slab.h> > #include <linux/rbtree.h> > #include <linux/spinlock.h> > +#include <linux/node.h> > #include <linux/nodemask.h> > #include <linux/pagemap.h> > #include <uapi/linux/mempolicy.h> > @@ -178,6 +179,9 @@ static inline bool mpol_is_preferred_many(struct mempolicy *pol) > > extern bool apply_policy_zone(struct mempolicy *policy, enum zone_type zone); > > +extern int mempolicy_set_node_perf(unsigned int node, > + struct access_coordinate *coords); > + > #else > > struct mempolicy {}; > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 04f35659717a..8777bd6229bc 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -109,6 +109,7 @@ > #include <linux/mmu_notifier.h> > #include <linux/printk.h> > #include <linux/swapops.h> > +#include <linux/gcd.h> > > #include <asm/tlbflush.h> > #include <asm/tlb.h> > @@ -138,16 +139,18 @@ static struct mempolicy default_policy = { > > static struct mempolicy preferred_node_policy[MAX_NUMNODES]; > > +static uint64_t *node_bw_table; > + > /* > - * iw_table is the sysfs-set interleave weight table, a value of 0 denotes > - * system-default value should be used. A NULL iw_table also denotes that > - * system-default values should be used. Until the system-default table > - * is implemented, the system-default is always 1. > - * > + * iw_table is the interleave weight table. > + * If bandwiddth data is available and the user is in auto mode, the table > + * is populated with default values in [1,255]. > * iw_table is RCU protected > */ > static u8 __rcu *iw_table; > static DEFINE_MUTEX(iw_table_lock); > +static const int weightiness = 32; > +static bool weighted_interleave_auto = true; I still prefer to use 2 iw_table, one is for default, the other is for manual. The default one will be used if the manual one is NULL. Both are protected by RCU. The default one can be updated upon hotplug blindly. This makes the whole model easier to be understood IMHO. What do you think about that. > static u8 get_il_weight(int node) > { > @@ -156,14 +159,113 @@ static u8 get_il_weight(int node) > > rcu_read_lock(); > table = rcu_dereference(iw_table); > - /* if no iw_table, use system default */ > weight = table ? table[node] : 1; > - /* if value in iw_table is 0, use system default */ > - weight = weight ? weight : 1; > rcu_read_unlock(); > return weight; > } [snip] --- Best Regards, Huang, Ying
