Re: [PATCH] zsmalloc: zs_page_migrate: not check inuse if migrate_mode is not MIGRATE_ASYNC
From: Hui Zhu
Date: Thu Jul 20 2017 - 02:41:10 EST
Hi Minchan,
I am sorry for answer late.
I spent some time on ubuntu 16.04 with mmtests in an old laptop.
2017-07-17 13:39 GMT+08:00 Minchan Kim <minchan@xxxxxxxxxx>:
> Hello Hui,
>
> On Fri, Jul 14, 2017 at 03:51:07PM +0800, Hui Zhu wrote:
>> Got some -EBUSY from zs_page_migrate that will make migration
>> slow (retry) or fail (zs_page_putback will schedule_work free_work,
>> but it cannot ensure the success).
>
> I think EAGAIN(migration retrial) is better than EBUSY(bailout) because
> expectation is that zsmalloc will release the empty zs_page soon so
> at next retrial, it will be succeeded.
I am not sure.
This is the call trace of zs_page_migrate:
zs_page_migrate
mapping->a_ops->migratepage
move_to_new_page
__unmap_and_move
unmap_and_move
migrate_pages
In unmap_and_move will remove page from migration page list
and call putback_movable_page(will call mapping->a_ops->putback_page) if
return value of zs_page_migrate is not -EAGAIN.
The comments of this part:
After called mapping->a_ops->putback_page, zsmalloc can free the page
from ZS_EMPTY list.
If retrun -EAGAIN, the page will be not be put back. EAGAIN page will
be try again in migrate_pages without re-isolate.
> About schedule_work, as you said, we don't make sure when it happens but
> I believe it will happen in a migration iteration most of case.
> How often do you see that case?
I noticed this issue because my Kernel patch https://lkml.org/lkml/2014/5/28/113
that will remove retry in __alloc_contig_migrate_range.
This retry willhandle the -EBUSY because it will re-isolate the page
and re-call migrate_pages.
Without it will make cma_alloc fail at once with -EBUSY.
>
>>
>> And I didn't find anything that make zs_page_migrate cannot work with
>> a ZS_EMPTY zspage.
>> So make the patch to not check inuse if migrate_mode is not
>> MIGRATE_ASYNC.
>
> At a first glance, I think it work but the question is that it a same problem
> ith schedule_work of zs_page_putback. IOW, Until the work is done, compaction
> cannot succeed. Do you have any number before and after?
>
Following is what I got with highalloc-performance in a vbox with 2
cpu 1G memory 512 zram as swap:
ori afte
orig after
Minor Faults 50805113 50801261
Major Faults 43918 46692
Swap Ins 42087 46299
Swap Outs 89718 105495
Allocation stalls 0 0
DMA allocs 57787 69787
DMA32 allocs 47964599 47983772
Normal allocs 0 0
Movable allocs 0 0
Direct pages scanned 45493 28837
Kswapd pages scanned 1565222 1512947
Kswapd pages reclaimed 1342222 1334030
Direct pages reclaimed 45615 30174
Kswapd efficiency 85% 88%
Kswapd velocity 1897.101 1708.309
Direct efficiency 100% 104%
Direct velocity 55.139 32.561
Percentage direct scans 2% 1%
Zone normal velocity 1952.240 1740.870
Zone dma32 velocity 0.000 0.000
Zone dma velocity 0.000 0.000
Page writes by reclaim 89764.000 106043.000
Page writes file 46 548
Page writes anon 89718 105495
Page reclaim immediate 21457 7269
Sector Reads 3259688 3144160
Sector Writes 3667252 3675528
Page rescued immediate 0 0
Slabs scanned 1042872 1035438
Direct inode steals 8042 7772
Kswapd inode steals 54295 55075
Kswapd skipped wait 0 0
THP fault alloc 175 200
THP collapse alloc 226 363
THP splits 0 0
THP fault fallback 11 1
THP collapse fail 3 1
Compaction stalls 536 647
Compaction success 322 384
Compaction failures 214 263
Page migrate success 119608 127002
Page migrate failure 2723 2309
Compaction pages isolated 250179 265318
Compaction migrate scanned 9131832 9351314
Compaction free scanned 2093272 3059014
Compaction cost 192 202
NUMA alloc hit 47124555 47086375
NUMA alloc miss 0 0
NUMA interleave hit 0 0
NUMA alloc local 47124555 47086375
NUMA base PTE updates 0 0
NUMA huge PMD updates 0 0
NUMA page range updates 0 0
NUMA hint faults 0 0
NUMA hint local faults 0 0
NUMA hint local percent 100 100
NUMA pages migrated 0 0
AutoNUMA cost 0% 0%
It looks Page migrate success is increased.
Thanks,
Hui
> Thanks.
>
>>
>> Signed-off-by: Hui Zhu <zhuhui@xxxxxxxxxx>
>> ---
>> mm/zsmalloc.c | 66 +++++++++++++++++++++++++++++++++--------------------------
>> 1 file changed, 37 insertions(+), 29 deletions(-)
>>
>> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
>> index d41edd2..c298e5c 100644
>> --- a/mm/zsmalloc.c
>> +++ b/mm/zsmalloc.c
>> @@ -1982,6 +1982,7 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
>> unsigned long old_obj, new_obj;
>> unsigned int obj_idx;
>> int ret = -EAGAIN;
>> + int inuse;
>>
>> VM_BUG_ON_PAGE(!PageMovable(page), page);
>> VM_BUG_ON_PAGE(!PageIsolated(page), page);
>> @@ -1996,21 +1997,24 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
>> offset = get_first_obj_offset(page);
>>
>> spin_lock(&class->lock);
>> - if (!get_zspage_inuse(zspage)) {
>> + inuse = get_zspage_inuse(zspage);
>> + if (mode == MIGRATE_ASYNC && !inuse) {
>> ret = -EBUSY;
>> goto unlock_class;
>> }
>>
>> pos = offset;
>> s_addr = kmap_atomic(page);
>> - while (pos < PAGE_SIZE) {
>> - head = obj_to_head(page, s_addr + pos);
>> - if (head & OBJ_ALLOCATED_TAG) {
>> - handle = head & ~OBJ_ALLOCATED_TAG;
>> - if (!trypin_tag(handle))
>> - goto unpin_objects;
>> + if (inuse) {
>> + while (pos < PAGE_SIZE) {
>> + head = obj_to_head(page, s_addr + pos);
>> + if (head & OBJ_ALLOCATED_TAG) {
>> + handle = head & ~OBJ_ALLOCATED_TAG;
>> + if (!trypin_tag(handle))
>> + goto unpin_objects;
>> + }
>> + pos += class->size;
>> }
>> - pos += class->size;
>> }
>>
>> /*
>> @@ -2020,20 +2024,22 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
>> memcpy(d_addr, s_addr, PAGE_SIZE);
>> kunmap_atomic(d_addr);
>>
>> - for (addr = s_addr + offset; addr < s_addr + pos;
>> - addr += class->size) {
>> - head = obj_to_head(page, addr);
>> - if (head & OBJ_ALLOCATED_TAG) {
>> - handle = head & ~OBJ_ALLOCATED_TAG;
>> - if (!testpin_tag(handle))
>> - BUG();
>> -
>> - old_obj = handle_to_obj(handle);
>> - obj_to_location(old_obj, &dummy, &obj_idx);
>> - new_obj = (unsigned long)location_to_obj(newpage,
>> - obj_idx);
>> - new_obj |= BIT(HANDLE_PIN_BIT);
>> - record_obj(handle, new_obj);
>> + if (inuse) {
>> + for (addr = s_addr + offset; addr < s_addr + pos;
>> + addr += class->size) {
>> + head = obj_to_head(page, addr);
>> + if (head & OBJ_ALLOCATED_TAG) {
>> + handle = head & ~OBJ_ALLOCATED_TAG;
>> + if (!testpin_tag(handle))
>> + BUG();
>> +
>> + old_obj = handle_to_obj(handle);
>> + obj_to_location(old_obj, &dummy, &obj_idx);
>> + new_obj = (unsigned long)
>> + location_to_obj(newpage, obj_idx);
>> + new_obj |= BIT(HANDLE_PIN_BIT);
>> + record_obj(handle, new_obj);
>> + }
>> }
>> }
>>
>> @@ -2055,14 +2061,16 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
>>
>> ret = MIGRATEPAGE_SUCCESS;
>> unpin_objects:
>> - for (addr = s_addr + offset; addr < s_addr + pos;
>> + if (inuse) {
>> + for (addr = s_addr + offset; addr < s_addr + pos;
>> addr += class->size) {
>> - head = obj_to_head(page, addr);
>> - if (head & OBJ_ALLOCATED_TAG) {
>> - handle = head & ~OBJ_ALLOCATED_TAG;
>> - if (!testpin_tag(handle))
>> - BUG();
>> - unpin_tag(handle);
>> + head = obj_to_head(page, addr);
>> + if (head & OBJ_ALLOCATED_TAG) {
>> + handle = head & ~OBJ_ALLOCATED_TAG;
>> + if (!testpin_tag(handle))
>> + BUG();
>> + unpin_tag(handle);
>> + }
>> }
>> }
>> kunmap_atomic(s_addr);
>> --
>> 1.9.1
>>
>> --
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