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Message-ID: <59c7f8c7-d2ef-8b59-637e-88a353d4daf0@linux.alibaba.com>
Date: Wed, 11 Mar 2020 20:00:08 +0800
From: Shile Zhang <shile.zhang@...ux.alibaba.com>
To: Kirill Tkhai <ktkhai@...tuozzo.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Pavel Tatashin <pasha.tatashin@...een.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Vlastimil Babka <vbabka@...e.cz>,
Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v2 1/1] mm: fix interrupt disabled long time inside
deferred_init_memmap()
On 2020/3/11 19:42, Kirill Tkhai wrote:
> On 11.03.2020 04:44, Shile Zhang wrote:
>> Hi Kirill,
>>
>> Sorry for late to reply!
>> I'm not fully understood the whole thing about deferred page init, so I
>> just force on the jiffies update issue itself.
>>
>> Maybe I'm in wrong path, it seems make no sense that deferred page init in 1 CPU system,
>> it cannot be initialize memory parallel.
> Yes, it can't be initialized in parallel. But scheduler interprets deferred thread as a separate
> task, so CPU time will be shared between that thread and the rest of tasks. This still should
> make boot faster.
Thanks for your quickly reply!
Sorry, I don't think the CPU time can be shared to the rest of tasks
since the CPU be blocked until
the deferred pages are all initialized, as following code:
8<------
#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
/* There will be num_node_state(N_MEMORY) threads */
atomic_set(&pgdat_init_n_undone, num_node_state(N_MEMORY));
for_each_node_state(nid, N_MEMORY) {
kthread_run(deferred_init_memmap, NODE_DATA(nid),
"pgdatinit%d", nid);
}
/* Block until all are initialised */
wait_for_completion(&pgdat_init_all_done_comp);
8<-------
Maybe I misunderstood this point.
@Pavel,
Could you please give any advice on this point? Thanks!
>> It might be better to disable deferred page init in 'deferred_init' in case of 1 CPU
>> (or only one memory node).
>>
>> In other word, seems the better way to solve this issue is do not bind 'pgdatinit' thread
>> on boot CPU.
>>
>> I also refactor the patch based on your comment, please help to check, thanks!
>>
>>
>> On 2020/3/4 18:47, Kirill Tkhai wrote:
>>> On 04.03.2020 05:34, Shile Zhang wrote:
>>>> Hi Kirill,
>>>>
>>>> Thanks for your quickly reply!
>>>>
>>>> On 2020/3/4 00:52, Kirill Tkhai wrote:
>>>>> On 03.03.2020 19:15, Shile Zhang wrote:
>>>>>> When 'CONFIG_DEFERRED_STRUCT_PAGE_INIT' is set, 'pgdatinit' kthread will
>>>>>> initialise the deferred pages with local interrupts disabled. It is
>>>>>> introduced by commit 3a2d7fa8a3d5 ("mm: disable interrupts while
>>>>>> initializing deferred pages").
>>>>>>
>>>>>> The local interrupt will be disabled long time inside
>>>>>> deferred_init_memmap(), depends on memory size.
>>>>>> On machine with NCPUS <= 2, the 'pgdatinit' kthread could be pined on
>>>>>> boot CPU, then the tick timer will stuck long time, which caused the
>>>>>> system wall time inaccuracy.
>>>>>>
>>>>>> For example, the dmesg shown that:
>>>>>>
>>>>>> [ 0.197975] node 0 initialised, 32170688 pages in 1ms
>>>>>>
>>>>>> Obviously, 1ms is unreasonable.
>>>>>> Now, fix it by restore in the pending interrupts inside the while loop.
>>>>>> The reasonable demsg shown likes:
>>>>>>
>>>>>> [ 1.069306] node 0 initialised, 32203456 pages in 894ms
>>>>> The way I understand the original problem, that Pavel fixed:
>>>>>
>>>>> we need disable irqs in deferred_init_memmap() since this function may be called
>>>>> in parallel with deferred_grow_zone() called from interrupt handler. So, Pavel
>>>>> added lock to fix the race.
>>>>>
>>>>> In case of we temporary unlock the lock, interrupt still be possible,
>>>>> so my previous proposition returns the problem back.
>>>>>
>>>>> Now thought again, I think we have to just add:
>>>>>
>>>>> pgdat_resize_unlock();
>>>>> pgdat_resize_lock();
>>>>>
>>>>> instead of releasing interrupts, since in case of we just release them with lock held,
>>>>> a call of interrupt->deferred_grow_zone() bring us to a deadlock.
>>>>>
>>>>> So, unlock the lock is must.
>>>> Yes, you're right! I missed this point.
>>>> Thanks for your comment!
>>>>
>>>>>> Signed-off-by: Shile Zhang<shile.zhang@...ux.alibaba.com>
>>>>>> ---
>>>>>> mm/page_alloc.c | 6 +++++-
>>>>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>>>> index 3c4eb750a199..d3f337f2e089 100644
>>>>>> --- a/mm/page_alloc.c
>>>>>> +++ b/mm/page_alloc.c
>>>>>> @@ -1809,8 +1809,12 @@ static int __init deferred_init_memmap(void *data)
>>>>>> * that we can avoid introducing any issues with the buddy
>>>>>> * allocator.
>>>>>> */
>>>>>> - while (spfn < epfn)
>>>>>> + while (spfn < epfn) {
>>>>>> nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
>>>>>> + /* let in any pending interrupts */
>>>>>> + local_irq_restore(flags);
>>>>>> + local_irq_save(flags);
>>>>>> + }
>>>>>> zone_empty:
>>>>>> pgdat_resize_unlock(pgdat, &flags);
>>>>> I think we need here something like below (untested):
>>>>>
>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>>> index 79e950d76ffc..323afa9a4db5 100644
>>>>> --- a/mm/page_alloc.c
>>>>> +++ b/mm/page_alloc.c
>>>>> @@ -1828,7 +1828,7 @@ static int __init deferred_init_memmap(void *data)
>>>>> {
>>>>> pg_data_t *pgdat = data;
>>>>> const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
>>>>> - unsigned long spfn = 0, epfn = 0, nr_pages = 0;
>>>>> + unsigned long spfn = 0, epfn = 0, nr_pages = 0, prev_nr_pages = 0;
>>>>> unsigned long first_init_pfn, flags;
>>>>> unsigned long start = jiffies;
>>>>> struct zone *zone;
>>>>> @@ -1869,8 +1869,18 @@ static int __init deferred_init_memmap(void *data)
>>>>> * that we can avoid introducing any issues with the buddy
>>>>> * allocator.
>>>>> */
>>>>> - while (spfn < epfn)
>>>>> + while (spfn < epfn) {
>>>>> nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
>>>>> + /*
>>>>> + * Release interrupts every 1Gb to give a possibility
>>>>> + * a timer to advance jiffies.
>>>>> + */
>>>>> + if (nr_pages - prev_nr_pages > (1UL << (30 - PAGE_SHIFT))) {
>>>>> + prev_nr_pages = nr_pages;
>>>>> + pgdat_resize_unlock(pgdat, &flags);
>>>>> + pgdat_resize_lock(pgdat, &flags);
>>>>> + }
>>>>> + }
>>>>> zone_empty:
>>>>> pgdat_resize_unlock(pgdat, &flags);
>>>>> (I believe the comment may be improved more).
>>>> Yeah, your patch is better!
>>>> I test your code and it works!
>>>> But it seems that 1G is still hold the interrupts too long, about 40ms in my env
>>>> with Intel(R) Xeon(R) 2.5GHz). I tried other size, it is OK to use 1024 pages (4MB),
>>>> which suggested by Andrew's before.
>>>>
>>>> Could you please help to review it again?
>>>>
>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>>> index 3c4eb750a199..5def66d3ffcd 100644
>>>> --- a/mm/page_alloc.c
>>>> +++ b/mm/page_alloc.c
>>>> @@ -1768,7 +1768,7 @@ static int __init deferred_init_memmap(void *data)
>>>> {
>>>> pg_data_t *pgdat = data;
>>>> const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
>>>> - unsigned long spfn = 0, epfn = 0, nr_pages = 0;
>>>> + unsigned long spfn = 0, epfn = 0, nr_pages = 0, prev_nr_pages = 0;
>>>> unsigned long first_init_pfn, flags;
>>>> unsigned long start = jiffies;
>>>> struct zone *zone;
>>>> @@ -1809,8 +1809,17 @@ static int __init deferred_init_memmap(void *data)
>>>> * that we can avoid introducing any issues with the buddy
>>>> * allocator.
>>>> */
>>>> - while (spfn < epfn)
>>>> + while (spfn < epfn) {
>>>> nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
>>>> + /*
>>>> + * Restore pending interrupts every 1024 pages to give
>>>> + * the chance tick timer to advance jiffies.
>>>> + */
>>>> + if (nr_pages - prev_nr_pages > 1024) {
>>>> + pgdat_resize_unlock(&flags);
>>>> + pgdat_resize_lock(&flags);
>>> Here is problem: prev_nr_pages must be updated.
>>>
>>> Anyway, releasing every 4M looks wrong for me, since you removes the fix that Pavel introduced.
>>> He protected against big allocations made from interrupt content. But in case of we unlock
>>> the lock after 4Mb, only 4Mb will be available for allocations from interrupts. pgdat->first_deferred_pfn
>>> is updated at the start of function, so interrupt allocations won't be able to initialize
>>> mode for themselve.
>> Yes, you're right. I missed this point since I'm not fully understood the code before.
>> Thanks for your advice!
>>> In case of you want unlock interrupts very often, you should make some creativity with first_deferred_pfn.
>>> We should update it sequentially. Something like below (untested):
>> I got your point now, thanks!
>>> ---
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 79e950d76ffc..be09d158baeb 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -1828,7 +1828,7 @@ static int __init deferred_init_memmap(void *data)
>>> {
>>> pg_data_t *pgdat = data;
>>> const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
>>> - unsigned long spfn = 0, epfn = 0, nr_pages = 0;
>>> + unsigned long spfn = 0, epfn = 0, nr_pages;
>>> unsigned long first_init_pfn, flags;
>>> unsigned long start = jiffies;
>>> struct zone *zone;
>>> @@ -1838,7 +1838,7 @@ static int __init deferred_init_memmap(void *data)
>>> /* Bind memory initialisation thread to a local node if possible */
>>> if (!cpumask_empty(cpumask))
>>> set_cpus_allowed_ptr(current, cpumask);
>>> -
>>> +again:
>>> pgdat_resize_lock(pgdat, &flags);
>>> first_init_pfn = pgdat->first_deferred_pfn;
>>> if (first_init_pfn == ULONG_MAX) {
>>> @@ -1850,7 +1850,6 @@ static int __init deferred_init_memmap(void *data)
>>> /* Sanity check boundaries */
>>> BUG_ON(pgdat->first_deferred_pfn < pgdat->node_start_pfn);
>>> BUG_ON(pgdat->first_deferred_pfn > pgdat_end_pfn(pgdat));
>>> - pgdat->first_deferred_pfn = ULONG_MAX;
>>> /* Only the highest zone is deferred so find it */
>>> for (zid = 0; zid < MAX_NR_ZONES; zid++) {
>>> @@ -1864,14 +1863,30 @@ static int __init deferred_init_memmap(void *data)
>>> first_init_pfn))
>>> goto zone_empty;
>>> + nr_pages = 0;
>> 'nr_pages' used to mark the total init pages before, so it cannot be zerolized each round.
>> seems we need one more to count the pages init each round.
>>
>>> +
>>> /*
>>> * Initialize and free pages in MAX_ORDER sized increments so
>>> * that we can avoid introducing any issues with the buddy
>>> * allocator.
>>> + * Final iteration marker is: spfn=ULONG_MAX and epfn=0.
>>> */
>>> - while (spfn < epfn)
>>> + while (spfn < epfn) {
>>> nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
>>> + if (!epfn)
>>> + break;
>> Seems 'epfn' never goes to 0 since it is "end page frame number", right?
>> So this is needless.
>>> + pgdat->first_deferred_pfn = epfn;
>> I think first_deferred_pfn update wrong value here, it seems should be the spfn, the start pfn right?
>>> + /*
>>> + * Restore pending interrupts every 128Mb to give
>>> + * the chance tick timer to advance jiffies.
>>> + */
>>> + if (nr_pages > (1UL << 27 - PAGE_SHIFT)) {
>>> + pgdat_resize_unlock(pgdat, &flags);
>>> + goto again;
>>> + }
>>> + }
>>> zone_empty:
>>> + pgdat->first_deferred_pfn = ULONG_MAX;
>>> pgdat_resize_unlock(pgdat, &flags);
>>> /* Sanity check that the next zone really is unpopulated */
>>>
>>>
>> I update the patch based on your comment, it passed the test.
>> Could you please help to review it again? Thanks!
> The patch is OK for me. It may be sent into ml with an appropriate description.
>
> Feel free to not forget to add my:
>
> Co-developed-by: Kirill Tkhai <ktkhai@...tuozzo.com>
Yeah, sure!
Many thanks for your kindly help on this issue!
I'll send out v3 later for further review.
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 3c4eb750a199..841c902d4509 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1763,12 +1763,17 @@ deferred_init_maxorder(u64 *i, struct zone *zone, unsigned long *start_pfn,
>> return nr_pages;
>> }
>>
>> +/*
>> + * Release the tick timer interrupts for every TICK_PAGE_COUNT pages.
>> + */
>> +#define TICK_PAGE_COUNT (32 * 1024)
>> +
>> /* Initialise remaining memory on a node */
>> static int __init deferred_init_memmap(void *data)
>> {
>> pg_data_t *pgdat = data;
>> const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
>> - unsigned long spfn = 0, epfn = 0, nr_pages = 0;
>> + unsigned long spfn = 0, epfn = 0, nr_pages = 0, prev_nr_pages = 0;
>> unsigned long first_init_pfn, flags;
>> unsigned long start = jiffies;
>> struct zone *zone;
>> @@ -1779,6 +1784,7 @@ static int __init deferred_init_memmap(void *data)
>> if (!cpumask_empty(cpumask))
>> set_cpus_allowed_ptr(current, cpumask);
>>
>> +again:
>> pgdat_resize_lock(pgdat, &flags);
>> first_init_pfn = pgdat->first_deferred_pfn;
>> if (first_init_pfn == ULONG_MAX) {
>> @@ -1790,7 +1796,6 @@ static int __init deferred_init_memmap(void *data)
>> /* Sanity check boundaries */
>> BUG_ON(pgdat->first_deferred_pfn < pgdat->node_start_pfn);
>> BUG_ON(pgdat->first_deferred_pfn > pgdat_end_pfn(pgdat));
>> - pgdat->first_deferred_pfn = ULONG_MAX;
>>
>> /* Only the highest zone is deferred so find it */
>> for (zid = 0; zid < MAX_NR_ZONES; zid++) {
>> @@ -1809,9 +1814,23 @@ static int __init deferred_init_memmap(void *data)
>> * that we can avoid introducing any issues with the buddy
>> * allocator.
>> */
>> - while (spfn < epfn)
>> + while (spfn < epfn) {
>> nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
>> + /*
>> + * Release the interrupts for every TICK_PAGE_COUNT pages
>> + * (128MB) to give the chance that tick timer to advance
>> + * the jiffies.
>> + */
>> + if ((nr_pages - prev_nr_pages) > TICK_PAGE_COUNT) {
>> + prev_nr_pages = nr_pages;
>> + pgdat->first_deferred_pfn = spfn;
>> + pgdat_resize_unlock(pgdat, &flags);
>> + goto again;
>> + }
>> + }
>> +
>> zone_empty:
>> + pgdat->first_deferred_pfn = ULONG_MAX;
>> pgdat_resize_unlock(pgdat, &flags);
>>
>> /* Sanity check that the next zone really is unpopulated */
>>
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