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Message-ID: <CAKPbEqpbtkbcH2XoV2g3AFm1HtzOPjkNMa3AyTqWdd5MyvY9pg@mail.gmail.com>
Date: Tue, 26 Mar 2024 23:55:07 -0700
From: "Ho-Ren (Jack) Chuang" <horenchuang@...edance.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Gregory Price <gourry.memverge@...il.com>, aneesh.kumar@...ux.ibm.com, mhocko@...e.com,
tj@...nel.org, john@...alactic.com, Eishan Mirakhur <emirakhur@...ron.com>,
Vinicius Tavares Petrucci <vtavarespetr@...ron.com>, Ravis OpenSrc <Ravis.OpenSrc@...ron.com>,
Alistair Popple <apopple@...dia.com>, Srinivasulu Thanneeru <sthanneeru@...ron.com>,
Dan Williams <dan.j.williams@...el.com>, Vishal Verma <vishal.l.verma@...el.com>,
Dave Jiang <dave.jiang@...el.com>, Andrew Morton <akpm@...ux-foundation.org>, nvdimm@...ts.linux.dev,
linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
"Ho-Ren (Jack) Chuang" <horenc@...edu>, "Ho-Ren (Jack) Chuang" <horenchuang@...il.com>, qemu-devel@...gnu.org,
Hao Xiang <hao.xiang@...edance.com>
Subject: Re: [External] Re: [PATCH v5 2/2] memory tier: create CPUless memory
tiers after obtaining HMAT info
On Tue, Mar 26, 2024 at 10:52 PM Huang, Ying <ying.huang@...el.com> wrote:
>
> "Ho-Ren (Jack) Chuang" <horenchuang@...edance.com> writes:
>
> > The current implementation treats emulated memory devices, such as
> > CXL1.1 type3 memory, as normal DRAM when they are emulated as normal memory
> > (E820_TYPE_RAM). However, these emulated devices have different
> > characteristics than traditional DRAM, making it important to
> > distinguish them. Thus, we modify the tiered memory initialization process
> > to introduce a delay specifically for CPUless NUMA nodes. This delay
> > ensures that the memory tier initialization for these nodes is deferred
> > until HMAT information is obtained during the boot process. Finally,
> > demotion tables are recalculated at the end.
> >
> > * late_initcall(memory_tier_late_init);
> > Some device drivers may have initialized memory tiers between
> > `memory_tier_init()` and `memory_tier_late_init()`, potentially bringing
> > online memory nodes and configuring memory tiers. They should be excluded
> > in the late init.
> >
> > * Handle cases where there is no HMAT when creating memory tiers
> > There is a scenario where a CPUless node does not provide HMAT information.
> > If no HMAT is specified, it falls back to using the default DRAM tier.
> >
> > * Introduce another new lock `default_dram_perf_lock` for adist calculation
> > In the current implementation, iterating through CPUlist nodes requires
> > holding the `memory_tier_lock`. However, `mt_calc_adistance()` will end up
> > trying to acquire the same lock, leading to a potential deadlock.
> > Therefore, we propose introducing a standalone `default_dram_perf_lock` to
> > protect `default_dram_perf_*`. This approach not only avoids deadlock
> > but also prevents holding a large lock simultaneously. Besides, this patch
> > slightly shortens the time holding the lock by putting the lock closer to
> > what it protects as well.
> >
> > * Upgrade `set_node_memory_tier` to support additional cases, including
> > default DRAM, late CPUless, and hot-plugged initializations.
> > To cover hot-plugged memory nodes, `mt_calc_adistance()` and
> > `mt_find_alloc_memory_type()` are moved into `set_node_memory_tier()` to
> > handle cases where memtype is not initialized and where HMAT information is
> > available.
> >
> > * Introduce `default_memory_types` for those memory types that are not
> > initialized by device drivers.
> > Because late initialized memory and default DRAM memory need to be managed,
> > a default memory type is created for storing all memory types that are
> > not initialized by device drivers and as a fallback.
> >
> > * Fix a deadlock bug in `mt_perf_to_adistance`
> > Because an error path was not handled properly in `mt_perf_to_adistance`,
> > unlock before returning the error.
> >
> > Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@...edance.com>
> > Signed-off-by: Hao Xiang <hao.xiang@...edance.com>
> > ---
> > mm/memory-tiers.c | 85 +++++++++++++++++++++++++++++++++++++++--------
> > 1 file changed, 72 insertions(+), 13 deletions(-)
> >
> > diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> > index 974af10cfdd8..610db9581ba4 100644
> > --- a/mm/memory-tiers.c
> > +++ b/mm/memory-tiers.c
> > @@ -36,6 +36,11 @@ struct node_memory_type_map {
> >
> > static DEFINE_MUTEX(memory_tier_lock);
> > static LIST_HEAD(memory_tiers);
> > +/*
> > + * The list is used to store all memory types that are not created
> > + * by a device driver.
> > + */
> > +static LIST_HEAD(default_memory_types);
> > static struct node_memory_type_map node_memory_types[MAX_NUMNODES];
> > struct memory_dev_type *default_dram_type;
> >
> > @@ -108,6 +113,8 @@ static struct demotion_nodes *node_demotion __read_mostly;
> >
> > static BLOCKING_NOTIFIER_HEAD(mt_adistance_algorithms);
> >
> > +/* The lock is used to protect `default_dram_perf*` info and nid. */
> > +static DEFINE_MUTEX(default_dram_perf_lock);
> > static bool default_dram_perf_error;
> > static struct access_coordinate default_dram_perf;
> > static int default_dram_perf_ref_nid = NUMA_NO_NODE;
> > @@ -505,7 +512,8 @@ static inline void __init_node_memory_type(int node, struct memory_dev_type *mem
> > static struct memory_tier *set_node_memory_tier(int node)
> > {
> > struct memory_tier *memtier;
> > - struct memory_dev_type *memtype;
> > + struct memory_dev_type *mtype = default_dram_type;
> > + int adist = MEMTIER_ADISTANCE_DRAM;
> > pg_data_t *pgdat = NODE_DATA(node);
> >
> >
> > @@ -514,11 +522,20 @@ static struct memory_tier *set_node_memory_tier(int node)
> > if (!node_state(node, N_MEMORY))
> > return ERR_PTR(-EINVAL);
> >
> > - __init_node_memory_type(node, default_dram_type);
> > + mt_calc_adistance(node, &adist);
> > + if (node_memory_types[node].memtype == NULL) {
> > + mtype = mt_find_alloc_memory_type(adist, &default_memory_types);
> > + if (IS_ERR(mtype)) {
> > + mtype = default_dram_type;
> > + pr_info("Failed to allocate a memory type. Fall back.\n");
> > + }
> > + }
> >
> > - memtype = node_memory_types[node].memtype;
> > - node_set(node, memtype->nodes);
> > - memtier = find_create_memory_tier(memtype);
> > + __init_node_memory_type(node, mtype);
> > +
> > + mtype = node_memory_types[node].memtype;
> > + node_set(node, mtype->nodes);
> > + memtier = find_create_memory_tier(mtype);
> > if (!IS_ERR(memtier))
> > rcu_assign_pointer(pgdat->memtier, memtier);
> > return memtier;
> > @@ -655,6 +672,34 @@ void mt_put_memory_types(struct list_head *memory_types)
> > }
> > EXPORT_SYMBOL_GPL(mt_put_memory_types);
> >
> > +/*
> > + * This is invoked via `late_initcall()` to initialize memory tiers for
> > + * CPU-less memory nodes after driver initialization, which is
> > + * expected to provide `adistance` algorithms.
> > + */
> > +static int __init memory_tier_late_init(void)
> > +{
> > + int nid;
> > +
> > + mutex_lock(&memory_tier_lock);
> > + for_each_node_state(nid, N_MEMORY)
> > + if (!node_state(nid, N_CPU) &&
> > + node_memory_types[nid].memtype == NULL)
> > + /*
> > + * Some device drivers may have initialized memory tiers
> > + * between `memory_tier_init()` and `memory_tier_late_init()`,
> > + * potentially bringing online memory nodes and
> > + * configuring memory tiers. Exclude them here.
> > + */
> > + set_node_memory_tier(nid);
> > +
> > + establish_demotion_targets();
> > + mutex_unlock(&memory_tier_lock);
> > +
> > + return 0;
> > +}
> > +late_initcall(memory_tier_late_init);
> > +
> > static void dump_hmem_attrs(struct access_coordinate *coord, const char *prefix)
> > {
> > pr_info(
> > @@ -668,7 +713,6 @@ int mt_set_default_dram_perf(int nid, struct access_coordinate *perf,
> > {
> > int rc = 0;
> >
> > - mutex_lock(&memory_tier_lock);
> > if (default_dram_perf_error) {
> > rc = -EIO;
> > goto out;
> > @@ -680,6 +724,7 @@ int mt_set_default_dram_perf(int nid, struct access_coordinate *perf,
> > goto out;
> > }
> >
> > + mutex_lock(&default_dram_perf_lock);
>
> Why do you move the position of locking? mutex_lock/unlock() will be
> unbalance for error path above.
>
Because you've mentioned below that moving the lock to the
beginning of the function will make the code easier to understand,
I will move the lock to the beginning of the function.
Perhaps the explanation may no longer be relevant; because reading
`default_dram_perf_error` and `perf->*` do not require
holding `default_dram_perf_lock`, but I forgot to replace
"rc = -EXXX ; goto out;" with return -EXXX.
> > if (default_dram_perf_ref_nid == NUMA_NO_NODE) {
> > default_dram_perf = *perf;
> > default_dram_perf_ref_nid = nid;
> > @@ -716,23 +761,26 @@ int mt_set_default_dram_perf(int nid, struct access_coordinate *perf,
> > }
> >
> > out:
> > - mutex_unlock(&memory_tier_lock);
> > + mutex_unlock(&default_dram_perf_lock);
> > return rc;
> > }
> >
> > int mt_perf_to_adistance(struct access_coordinate *perf, int *adist)
> > {
> > + int rc = 0;
> > +
> > if (default_dram_perf_error)
> > return -EIO;
> >
> > - if (default_dram_perf_ref_nid == NUMA_NO_NODE)
> > - return -ENOENT;
> > -
> > if (perf->read_latency + perf->write_latency == 0 ||
> > perf->read_bandwidth + perf->write_bandwidth == 0)
> > return -EINVAL;
> >
> > - mutex_lock(&memory_tier_lock);
> > + mutex_lock(&default_dram_perf_lock);
>
> It may be a little better to move lock position at the begin of the
> function. This will not avoid race condition (not harmful in practice)
> but it will make code easier to be understood.
>
No problem. I will move the lock to the beginning of the function and
take care of all error paths.
> > + if (default_dram_perf_ref_nid == NUMA_NO_NODE) {
> > + rc = -ENOENT;
> > + goto out;
> > + }
> > /*
> > * The abstract distance of a memory node is in direct proportion to
> > * its memory latency (read + write) and inversely proportional to its
> > @@ -745,8 +793,10 @@ int mt_perf_to_adistance(struct access_coordinate *perf, int *adist)
> > (default_dram_perf.read_latency + default_dram_perf.write_latency) *
> > (default_dram_perf.read_bandwidth + default_dram_perf.write_bandwidth) /
> > (perf->read_bandwidth + perf->write_bandwidth);
> > - mutex_unlock(&memory_tier_lock);
> > + mutex_unlock(&default_dram_perf_lock);
> >
> > +out:
> > + mutex_unlock(&default_dram_perf_lock);
> > return 0;
> > }
> > EXPORT_SYMBOL_GPL(mt_perf_to_adistance);
> > @@ -858,7 +908,8 @@ static int __init memory_tier_init(void)
> > * For now we can have 4 faster memory tiers with smaller adistance
> > * than default DRAM tier.
> > */
> > - default_dram_type = alloc_memory_type(MEMTIER_ADISTANCE_DRAM);
> > + default_dram_type = mt_find_alloc_memory_type(MEMTIER_ADISTANCE_DRAM,
> > + &default_memory_types);
> > if (IS_ERR(default_dram_type))
> > panic("%s() failed to allocate default DRAM tier\n", __func__);
> >
> > @@ -868,6 +919,14 @@ static int __init memory_tier_init(void)
> > * types assigned.
> > */
> > for_each_node_state(node, N_MEMORY) {
> > + if (!node_state(node, N_CPU))
> > + /*
> > + * Defer memory tier initialization on CPUless numa nodes.
> > + * These will be initialized after firmware and devices are
> > + * initialized.
> > + */
> > + continue;
> > +
> > memtier = set_node_memory_tier(node);
> > if (IS_ERR(memtier))
> > /*
>
> --
> Best Regards,
> Huang, Ying
--
Best regards,
Ho-Ren (Jack) Chuang
莊賀任
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