| Message ID | 1685501461-19290-1-git-send-email-zhaoyang.huang@unisoc.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [PATCHv5] mm: skip CMA pages when they are not available | expand |
On Wed, 31 May 2023 10:51:01 +0800 "zhaoyang.huang" <zhaoyang.huang@unisoc.com> wrote: > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > This patch fixes unproductive reclaiming of CMA pages by skipping them when they > are not available for current context. It is arise from bellowing OOM issue, which > caused by large proportion of MIGRATE_CMA pages among free pages. > > [ 36.172486] [03-19 10:05:52.172] ActivityManager: page allocation failure: order:0, mode:0xc00(GFP_NOIO), nodemask=(null),cpuset=foreground,mems_allowed=0 > [ 36.189447] [03-19 10:05:52.189] DMA32: 0*4kB 447*8kB (C) 217*16kB (C) 124*32kB (C) 136*64kB (C) 70*128kB (C) 22*256kB (C) 3*512kB (C) 0*1024kB 0*2048kB 0*4096kB = 35848kB > [ 36.193125] [03-19 10:05:52.193] Normal: 231*4kB (UMEH) 49*8kB (MEH) 14*16kB (H) 13*32kB (H) 8*64kB (H) 2*128kB (H) 0*256kB 1*512kB (H) 0*1024kB 0*2048kB 0*4096kB = 3236kB > ... > [ 36.234447] [03-19 10:05:52.234] SLUB: Unable to allocate memory on node -1, gfp=0xa20(GFP_ATOMIC) > [ 36.234455] [03-19 10:05:52.234] cache: ext4_io_end, object size: 64, buffer size: 64, default order: 0, min order: 0 > [ 36.234459] [03-19 10:05:52.234] node 0: slabs: 53,objs: 3392, free: 0 > We saw plenty of feedback for earlier versions, but now silence. Does this mean we're all OK with v5?
On Fri, Jun 09, 2023 at 03:35:19PM -0700, Andrew Morton wrote: > > This patch fixes unproductive reclaiming of CMA pages by skipping them when they > > are not available for current context. It is arise from bellowing OOM issue, which > > caused by large proportion of MIGRATE_CMA pages among free pages. > > We saw plenty of feedback for earlier versions, but now silence. Does > this mean we're all OK with v5? I'm fine with the implementation now. I have no idea if this is the right approach.
On 10.06.23 00:35, Andrew Morton wrote: > On Wed, 31 May 2023 10:51:01 +0800 "zhaoyang.huang" <zhaoyang.huang@unisoc.com> wrote: > >> From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> >> >> This patch fixes unproductive reclaiming of CMA pages by skipping them when they >> are not available for current context. It is arise from bellowing OOM issue, which >> caused by large proportion of MIGRATE_CMA pages among free pages. >> >> [ 36.172486] [03-19 10:05:52.172] ActivityManager: page allocation failure: order:0, mode:0xc00(GFP_NOIO), nodemask=(null),cpuset=foreground,mems_allowed=0 >> [ 36.189447] [03-19 10:05:52.189] DMA32: 0*4kB 447*8kB (C) 217*16kB (C) 124*32kB (C) 136*64kB (C) 70*128kB (C) 22*256kB (C) 3*512kB (C) 0*1024kB 0*2048kB 0*4096kB = 35848kB >> [ 36.193125] [03-19 10:05:52.193] Normal: 231*4kB (UMEH) 49*8kB (MEH) 14*16kB (H) 13*32kB (H) 8*64kB (H) 2*128kB (H) 0*256kB 1*512kB (H) 0*1024kB 0*2048kB 0*4096kB = 3236kB >> ... >> [ 36.234447] [03-19 10:05:52.234] SLUB: Unable to allocate memory on node -1, gfp=0xa20(GFP_ATOMIC) >> [ 36.234455] [03-19 10:05:52.234] cache: ext4_io_end, object size: 64, buffer size: 64, default order: 0, min order: 0 >> [ 36.234459] [03-19 10:05:52.234] node 0: slabs: 53,objs: 3392, free: 0 >> > > We saw plenty of feedback for earlier versions, but now silence. Does > this mean we're all OK with v5? The logic kind-of makes sense to me (but the kswapd special-casing already shows that it might be a bit fragile for future use), but I did not yet figure out if this actually fixes something or is a pure performance improvement. As we phrased it in the comment "It is waste of effort", but in the patch description "This patch fixes unproductive reclaiming" + a scary dmesg. Am I correct that this is a pure performance optimization (and the issue revealed itself in that OOM report), or does this actually *fix* something? If it's a performance improvement, it would be good to show that it is an actual improvement worth the churn ...
On Mon, Jun 12, 2023 at 5:29 PM David Hildenbrand <david@redhat.com> wrote: > > On 10.06.23 00:35, Andrew Morton wrote: > > On Wed, 31 May 2023 10:51:01 +0800 "zhaoyang.huang" <zhaoyang.huang@unisoc.com> wrote: > > > >> From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > >> > >> This patch fixes unproductive reclaiming of CMA pages by skipping them when they > >> are not available for current context. It is arise from bellowing OOM issue, which > >> caused by large proportion of MIGRATE_CMA pages among free pages. > >> > >> [ 36.172486] [03-19 10:05:52.172] ActivityManager: page allocation failure: order:0, mode:0xc00(GFP_NOIO), nodemask=(null),cpuset=foreground,mems_allowed=0 > >> [ 36.189447] [03-19 10:05:52.189] DMA32: 0*4kB 447*8kB (C) 217*16kB (C) 124*32kB (C) 136*64kB (C) 70*128kB (C) 22*256kB (C) 3*512kB (C) 0*1024kB 0*2048kB 0*4096kB = 35848kB > >> [ 36.193125] [03-19 10:05:52.193] Normal: 231*4kB (UMEH) 49*8kB (MEH) 14*16kB (H) 13*32kB (H) 8*64kB (H) 2*128kB (H) 0*256kB 1*512kB (H) 0*1024kB 0*2048kB 0*4096kB = 3236kB > >> ... > >> [ 36.234447] [03-19 10:05:52.234] SLUB: Unable to allocate memory on node -1, gfp=0xa20(GFP_ATOMIC) > >> [ 36.234455] [03-19 10:05:52.234] cache: ext4_io_end, object size: 64, buffer size: 64, default order: 0, min order: 0 > >> [ 36.234459] [03-19 10:05:52.234] node 0: slabs: 53,objs: 3392, free: 0 > >> > > > > We saw plenty of feedback for earlier versions, but now silence. Does > > this mean we're all OK with v5? > > The logic kind-of makes sense to me (but the kswapd special-casing > already shows that it might be a bit fragile for future use), but I did > not yet figure out if this actually fixes something or is a pure > performance improvement. > > As we phrased it in the comment "It is waste of effort", but in the > patch description "This patch fixes unproductive reclaiming" + a scary > dmesg. > > Am I correct that this is a pure performance optimization (and the issue > revealed itself in that OOM report), or does this actually *fix* something? > > If it's a performance improvement, it would be good to show that it is > an actual improvement worth the churn ... Sorry for the confusion. As for the OOM issue, the previous commit(https://lkml.kernel.org/r/1683782550-25799-1-git-send-email-zhaoyang.huang@unisoc.com) helps to decrease the fail rate from 12/20 to 2/20, which it turn to be 0 when applying this patch. > > -- > Cheers, > > David / dhildenb >
On 12.06.23 11:35, Zhaoyang Huang wrote: > On Mon, Jun 12, 2023 at 5:29 PM David Hildenbrand <david@redhat.com> wrote: >> >> On 10.06.23 00:35, Andrew Morton wrote: >>> On Wed, 31 May 2023 10:51:01 +0800 "zhaoyang.huang" <zhaoyang.huang@unisoc.com> wrote: >>> >>>> From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> >>>> >>>> This patch fixes unproductive reclaiming of CMA pages by skipping them when they >>>> are not available for current context. It is arise from bellowing OOM issue, which >>>> caused by large proportion of MIGRATE_CMA pages among free pages. >>>> >>>> [ 36.172486] [03-19 10:05:52.172] ActivityManager: page allocation failure: order:0, mode:0xc00(GFP_NOIO), nodemask=(null),cpuset=foreground,mems_allowed=0 >>>> [ 36.189447] [03-19 10:05:52.189] DMA32: 0*4kB 447*8kB (C) 217*16kB (C) 124*32kB (C) 136*64kB (C) 70*128kB (C) 22*256kB (C) 3*512kB (C) 0*1024kB 0*2048kB 0*4096kB = 35848kB >>>> [ 36.193125] [03-19 10:05:52.193] Normal: 231*4kB (UMEH) 49*8kB (MEH) 14*16kB (H) 13*32kB (H) 8*64kB (H) 2*128kB (H) 0*256kB 1*512kB (H) 0*1024kB 0*2048kB 0*4096kB = 3236kB >>>> ... >>>> [ 36.234447] [03-19 10:05:52.234] SLUB: Unable to allocate memory on node -1, gfp=0xa20(GFP_ATOMIC) >>>> [ 36.234455] [03-19 10:05:52.234] cache: ext4_io_end, object size: 64, buffer size: 64, default order: 0, min order: 0 >>>> [ 36.234459] [03-19 10:05:52.234] node 0: slabs: 53,objs: 3392, free: 0 >>>> >>> >>> We saw plenty of feedback for earlier versions, but now silence. Does >>> this mean we're all OK with v5? >> >> The logic kind-of makes sense to me (but the kswapd special-casing >> already shows that it might be a bit fragile for future use), but I did >> not yet figure out if this actually fixes something or is a pure >> performance improvement. >> >> As we phrased it in the comment "It is waste of effort", but in the >> patch description "This patch fixes unproductive reclaiming" + a scary >> dmesg. >> >> Am I correct that this is a pure performance optimization (and the issue >> revealed itself in that OOM report), or does this actually *fix* something? >> >> If it's a performance improvement, it would be good to show that it is >> an actual improvement worth the churn ... > Sorry for the confusion. As for the OOM issue, the previous > commit(https://lkml.kernel.org/r/1683782550-25799-1-git-send-email-zhaoyang.huang@unisoc.com) > helps to decrease the fail rate from 12/20 to 2/20, which it turn to > be 0 when applying this patch. Thanks! Can we make that clearer in the patch description? I'm struggling a bit my self to find the right words. Something like "This change further decreases the chance for wrong OOMs in the presence of a lot of CMA memory." ? In any case Acked-by: David Hildenbrand <david@redhat.com>
On Mon, 12 Jun 2023 12:01:20 +0200 David Hildenbrand <david@redhat.com> wrote: > ... > > >> > >> If it's a performance improvement, it would be good to show that it is > >> an actual improvement worth the churn ... > > Sorry for the confusion. As for the OOM issue, the previous > > commit(https://lkml.kernel.org/r/1683782550-25799-1-git-send-email-zhaoyang.huang@unisoc.com) > > helps to decrease the fail rate from 12/20 to 2/20, which it turn to > > be 0 when applying this patch. > > Thanks! Can we make that clearer in the patch description? I'm > struggling a bit my self to find the right words. > > Something like > > "This change further decreases the chance for wrong OOMs in the presence > of a lot of CMA memory." > Great, I added that. > > In any case > > Acked-by: David Hildenbrand <david@redhat.com> > And I'll move this patch into mm-stable.
On Wed, May 31, 2023 at 10:51:01AM +0800, zhaoyang.huang wrote: > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > This patch fixes unproductive reclaiming of CMA pages by skipping them when they > are not available for current context. It is arise from bellowing OOM issue, which > caused by large proportion of MIGRATE_CMA pages among free pages. Hello, I've been looking into a problem with high memory pressure causing OOMs in some of our workloads, and it seems that this change may have introduced lock contention when there is high memory pressure. I've collected some metrics for my specific workload that suggest this change has increased the lruvec->lru_lock waittime-max by 500x and the waittime-avg by 20x. Experiment ========== The experiment involved 100 hosts, each with 64GB of memory and a single Xeon 8321HC CPU. The experiment ran for over 80 hours. Half of the hosts (50) were configured with the patch reverted and lock stat enabled, while the other half was run against the upstream version. All machines had hugetlb_cma=6G set as a command-line argument. In this context, "upstream" refers to kernel release 6.9 with some minor changes that should not impact the results. Workload ======== The workload is a Java based application that fully utilized the memory, in fact, the JVM runs with `-Xms50735m -Xmx50735m` arguments. Results: ======= A few values from lockstat: waittime-max waittime-total waittime-avg holdtime-max 6.9: 242889 15618873933 715 17485 6.9-with-revert: 487 688563299 34 464 The full data could be seen at: https://docs.google.com/spreadsheets/d/1Dl-8ImlE4OZrfKjbyWAIWWuQtgD3fwEEl9INaZQZ4e8/edit?usp=sharing Possible causes: ================ I've been discussing this with colleagues and we're speculating that the high contention might be linked to the fact that CMA regions are now being skipped. This could potentially extend the duration of the isolate_lru_folios() 'while' loop, resulting in increased pressure on the lock. However, I want to emphasize that I'm not an expert in this area and I am simply sharing the data I collected.
diff --git a/mm/vmscan.c b/mm/vmscan.c index bd6637f..972a54d 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2193,6 +2193,25 @@ static __always_inline void update_lru_sizes(struct lruvec *lruvec, } +#ifdef CONFIG_CMA +/* + * It is waste of effort to scan and reclaim CMA pages if it is not available + * for current allocation context. Kswapd can not be enrolled as it can not + * distinguish this scenario by using sc->gfp_mask = GFP_KERNEL + */ +static bool skip_cma(struct folio *folio, struct scan_control *sc) +{ + return !current_is_kswapd() && + gfp_migratetype(sc->gfp_mask) != MIGRATE_MOVABLE && + get_pageblock_migratetype(&folio->page) == MIGRATE_CMA; +} +#else +static bool skip_cma(struct folio *folio, struct scan_control *sc) +{ + return false; +} +#endif + /* * Isolating page from the lruvec to fill in @dst list by nr_to_scan times. * @@ -2239,7 +2258,8 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan, nr_pages = folio_nr_pages(folio); total_scan += nr_pages; - if (folio_zonenum(folio) > sc->reclaim_idx) { + if (folio_zonenum(folio) > sc->reclaim_idx || + skip_cma(folio, sc)) { nr_skipped[folio_zonenum(folio)] += nr_pages; move_to = &folios_skipped; goto move;