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Subject: Re: [PATCH] dma-buf: system_heap: avoid reclaim for order 4
Reply-To: jaewon31.kim@samsung.com
Sender: Jaewon Kim <jaewon31.kim@samsung.com>
From:   Jaewon Kim <jaewon31.kim@samsung.com>
To:     John Stultz <jstultz@google.com>
CC:     "sumit.semwal@linaro.org" <sumit.semwal@linaro.org>,
        "daniel.vetter@ffwll.ch" <daniel.vetter@ffwll.ch>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "hannes@cmpxchg.org" <hannes@cmpxchg.org>,
        "mhocko@kernel.org" <mhocko@kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "jaewon31.kim@gmail.com" <jaewon31.kim@gmail.com>,
        "T.J. Mercier" <tjmercier@google.com>
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Message-ID: <20230118073043epcms1p8b5cfde0d773e296770775581b6ce7105@epcms1p8>
Date:   Wed, 18 Jan 2023 16:30:43 +0900
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>On Tue, Jan 17, 2023 at 12:31 AM Jaewon Kim <jaewon31.kim@samsung.com> wrote:
>> > Using order 4 pages would be helpful for many IOMMUs, but it could spend
>> > quite much time in page allocation perspective.
>> >
>> > The order 4 allocation with __GFP_RECLAIM may spend much time in
>> > reclaim and compation logic. __GFP_NORETRY also may affect. These cause
>> > unpredictable delay.
>> >
>> > To get reasonable allocation speed from dma-buf system heap, use
>> > HIGH_ORDER_GFP for order 4 to avoid reclaim.
>
>Thanks for sharing this!
>The case where the allocation gets stuck behind reclaim under pressure
>does sound undesirable, but I'd be a bit hesitant to tweak numbers
>that have been used for a long while (going back to ion) without a bit
>more data.
>
>It might be good to also better understand the tradeoff of potential
>on-going impact to performance from using low order pages when the
>buffer is used.  Do you have any details like or tests that you could
>share to help ensure this won't impact other users?
>
>TJ: Do you have any additional thoughts on this?
>
>thanks
>-john

Let me share what I tested with trace events of compaction, direct_reclaim.
This log was captured within one dma-buf alloc for 1,957,888 byte size.
It shows direct reclaim spent 4.973 msec total so that it could reclaim 209 pages total.
But it spent 12.606 msec in compaction.
I might miss preempted time but I think compaction is quite time consuming job.

Sorry I don't know how much the current gfp is helpful to IOMMU.
I think the default should be set like my change to improve allocation,
and the current gfp could be set if need through other options like cmdline.

-5972    [006] ....  7971.248176: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x40000 free_pfn=0xffc00 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.248394: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xac800 free_pfn=0xffc00 zone_end=0x100000, mode=async status=contended      
-5972    [006] ....  7971.248399: mm_vmscan_direct_reclaim_begin: order=4 gfp_flags=GFP_HIGHUSER|__GFP_NOWARN|__GFP_COMP|__GFP_ZERO                              
-5972    [006] ....  7971.248922: mm_vmscan_direct_reclaim_end: nr_reclaimed=17                                                                                  
-5972    [006] ....  7971.248974: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0xacc00 free_pfn=0xffc00 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.249063: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xb5c00 free_pfn=0xffc00 zone_end=0x100000, mode=async status=contended      
-5972    [006] ....  7971.249067: mm_vmscan_direct_reclaim_begin: order=4 gfp_flags=GFP_HIGHUSER|__GFP_NOWARN|__GFP_COMP|__GFP_ZERO                              
-5972    [006] ....  7971.249768: mm_vmscan_direct_reclaim_end: nr_reclaimed=18                                                                                  
-5972    [006] ....  7971.249843: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0xb6000 free_pfn=0xafc00 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.249845: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xb6000 free_pfn=0xafc00 zone_end=0x100000, mode=async status=partial_skipped
-5972    [006] ....  7971.249849: mm_vmscan_direct_reclaim_begin: order=4 gfp_flags=GFP_HIGHUSER|__GFP_NOWARN|__GFP_COMP|__GFP_ZERO                              
-5972    [006] ....  7971.250116: mm_vmscan_direct_reclaim_end: nr_reclaimed=22                                                                                  
-5972    [006] ....  7971.250152: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x40000 free_pfn=0xaf800 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.250305: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xac400 free_pfn=0xaf800 zone_end=0x100000, mode=async status=success        
-5972    [006] ....  7971.250375: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0xac800 free_pfn=0xaf800 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.250380: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xaf800 free_pfn=0xaf800 zone_end=0x100000, mode=async status=partial_skipped
-5972    [006] ....  7971.250384: mm_vmscan_direct_reclaim_begin: order=4 gfp_flags=GFP_HIGHUSER|__GFP_NOWARN|__GFP_COMP|__GFP_ZERO                              
-5972    [006] ....  7971.250597: mm_vmscan_direct_reclaim_end: nr_reclaimed=20                                                                                  
-5972    [006] ....  7971.251289: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x40000 free_pfn=0xaf000 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.251497: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xac400 free_pfn=0xaf000 zone_end=0x100000, mode=async status=contended      
-5972    [006] ....  7971.251502: mm_vmscan_direct_reclaim_begin: order=4 gfp_flags=GFP_HIGHUSER|__GFP_NOWARN|__GFP_COMP|__GFP_ZERO                              
-5972    [006] ....  7971.251797: mm_vmscan_direct_reclaim_end: nr_reclaimed=22                                                                                  
-5972    [006] ....  7971.251890: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x5b400 free_pfn=0xb0400 zone_end=0x100000, mode=sync                      
-5972    [006] ....  7971.252740: mm_compaction_end: zone_start=0x40000 migrate_pfn=0x63800 free_pfn=0xb0400 zone_end=0x100000, mode=sync status=success         
-5972    [006] ....  7971.252774: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x63c00 free_pfn=0xb0000 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.253325: mm_compaction_end: zone_start=0x40000 migrate_pfn=0x74e20 free_pfn=0xade92 zone_end=0x100000, mode=async status=success        
-5972    [006] ....  7971.253333: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x83400 free_pfn=0xafc00 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.253683: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xac400 free_pfn=0xafc00 zone_end=0x100000, mode=async status=contended      
-5972    [006] ....  7971.253688: mm_vmscan_direct_reclaim_begin: order=4 gfp_flags=GFP_HIGHUSER|__GFP_NOWARN|__GFP_COMP|__GFP_ZERO                              
-5972    [006] ....  7971.254134: mm_vmscan_direct_reclaim_end: nr_reclaimed=22                                                                                  
-5972    [006] ....  7971.254206: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0xad000 free_pfn=0xafc00 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.254289: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xae1c0 free_pfn=0xae000 zone_end=0x100000, mode=async status=partial_skipped
-5972    [006] ....  7971.254304: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x40000 free_pfn=0xffc00 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.254510: mm_compaction_end: zone_start=0x40000 migrate_pfn=0x74db0 free_pfn=0xadcc1 zone_end=0x100000, mode=async status=success        
-5972    [006] ....  7971.254519: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x75000 free_pfn=0xffc00 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.254612: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xac400 free_pfn=0xffc00 zone_end=0x100000, mode=async status=contended      
-5972    [006] ....  7971.254617: mm_vmscan_direct_reclaim_begin: order=4 gfp_flags=GFP_HIGHUSER|__GFP_NOWARN|__GFP_COMP|__GFP_ZERO                              
-5972    [006] ....  7971.255303: mm_vmscan_direct_reclaim_end: nr_reclaimed=22                                                                                  
-5972    [006] ....  7971.255307: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x75000 free_pfn=0xffc00 zone_end=0x100000, mode=sync                      
-5972    [006] ....  7971.260198: mm_compaction_end: zone_start=0x40000 migrate_pfn=0x751e5 free_pfn=0xaa83f zone_end=0x100000, mode=sync status=success         
-5972    [006] ....  7971.260236: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x40000 free_pfn=0xffc00 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.260883: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xb5c00 free_pfn=0xffc00 zone_end=0x100000, mode=async status=contended      
-5972    [006] ....  7971.260891: mm_vmscan_direct_reclaim_begin: order=4 gfp_flags=GFP_HIGHUSER|__GFP_NOWARN|__GFP_COMP|__GFP_ZERO                              
-5972    [006] ....  7971.261174: mm_vmscan_direct_reclaim_end: nr_reclaimed=22                                                                                  
-5972    [006] ....  7971.261178: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x75000 free_pfn=0xffc00 zone_end=0x100000, mode=sync                      
-5972    [006] ....  7971.264861: mm_compaction_end: zone_start=0x40000 migrate_pfn=0x75681 free_pfn=0xffc00 zone_end=0x100000, mode=sync status=success         
-5972    [006] ....  7971.264873: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0xbbc00 free_pfn=0xffc00 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.264889: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xc1400 free_pfn=0xffc00 zone_end=0x100000, mode=async status=contended      
-5972    [006] ....  7971.264891: mm_vmscan_direct_reclaim_begin: order=4 gfp_flags=GFP_HIGHUSER|__GFP_NOWARN|__GFP_COMP|__GFP_ZERO                              
-5972    [006] ....  7971.265141: mm_vmscan_direct_reclaim_end: nr_reclaimed=22                                                                                  
-5972    [002] ....  7971.265585: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0xc1800 free_pfn=0xffc00 zone_end=0x100000, mode=async                     
-5972    [002] ....  7971.265669: mm_compaction_end: zone_start=0x40000 migrate_pfn=0xc2c00 free_pfn=0xffc00 zone_end=0x100000, mode=async status=contended      
-5972    [002] ....  7971.265678: mm_vmscan_direct_reclaim_begin: order=4 gfp_flags=GFP_HIGHUSER|__GFP_NOWARN|__GFP_COMP|__GFP_ZERO                              
-5972    [002] ....  7971.266987: mm_vmscan_direct_reclaim_end: nr_reclaimed=22                                                                                  
-5972    [006] ....  7971.267466: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x40000 free_pfn=0xffc00 zone_end=0x100000, mode=sync                      
-5972    [006] ....  7971.267778: mm_compaction_end: zone_start=0x40000 migrate_pfn=0x5d000 free_pfn=0xffc00 zone_end=0x100000, mode=sync status=success         
-5972    [006] ....  7971.267927: mm_compaction_begin: zone_start=0x40000 migrate_pfn=0x5c000 free_pfn=0xffc00 zone_end=0x100000, mode=async                     
-5972    [006] ....  7971.268092: mm_compaction_end: zone_start=0x40000 migrate_pfn=0x74d70 free_pfn=0xffc00 zone_end=0x100000, mode=async status=success        

Thank you
Jaewon Kim