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Message-ID: <60eb1dbd-b320-ce9b-34f5-bc2e8b6d660b@linux.alibaba.com>
Date: Mon, 8 Jul 2019 15:52:29 -0700
From: Yang Shi <yang.shi@...ux.alibaba.com>
To: rientjes@...gle.com, kirill.shutemov@...ux.intel.com,
mhocko@...e.com, hannes@...xchg.org, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2 -mm] mm: account lazy free pages separately
Hi guys,
Any comment on this series?
Thanks,
Yang
On 6/27/19 10:12 AM, Yang Shi wrote:
> When doing partial unmap to THP, the pages in the affected range would
> be considered to be reclaimable when memory pressure comes in. And,
> such pages would be put on deferred split queue and get minus from the
> memory statistics (i.e. /proc/meminfo).
>
> For example, when doing THP split test, /proc/meminfo would show:
>
> Before put on lazy free list:
> MemTotal: 45288336 kB
> MemFree: 43281376 kB
> MemAvailable: 43254048 kB
> ...
> Active(anon): 1096296 kB
> Inactive(anon): 8372 kB
> ...
> AnonPages: 1096264 kB
> ...
> AnonHugePages: 1056768 kB
>
> After put on lazy free list:
> MemTotal: 45288336 kB
> MemFree: 43282612 kB
> MemAvailable: 43255284 kB
> ...
> Active(anon): 1094228 kB
> Inactive(anon): 8372 kB
> ...
> AnonPages: 49668 kB
> ...
> AnonHugePages: 10240 kB
>
> The THPs confusingly look disappeared although they are still on LRU if
> you are not familair the tricks done by kernel.
>
> Accounted the lazy free pages to NR_LAZYFREE, and show them in meminfo
> and other places. With the change the /proc/meminfo would look like:
> Before put on lazy free list:
> AnonHugePages: 1056768 kB
> ShmemHugePages: 0 kB
> ShmemPmdMapped: 0 kB
> LazyFreePages: 0 kB
>
> After put on lazy free list:
> AnonHugePages: 10240 kB
> ShmemHugePages: 0 kB
> ShmemPmdMapped: 0 kB
> LazyFreePages: 1046528 kB
>
> And, this is also the preparation for the following patch to account
> lazy free pages to available memory.
>
> Here the lazyfree doesn't count MADV_FREE pages since they are not
> actually unmapped until they get reclaimed. And, they are put on
> inactive file LRU, so they have been accounted for available memory.
>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
> ---
> I'm not quite sure whether LazyFreePages is a good name or not since "Lazyfree"
> is typically referred to MADV_FREE pages. I could use a more spceific name,
> i.e. "DeferredSplitTHP" since it doesn't account MADV_FREE as explained in the
> commit log. But, a more general name would be good for including other type
> pages in the future.
>
> And, I'm also not sure if it is a good idea to show this in memcg stat or not.
>
> Documentation/filesystems/proc.txt | 12 ++++++++----
> drivers/base/node.c | 3 +++
> fs/proc/meminfo.c | 3 +++
> include/linux/mmzone.h | 1 +
> mm/huge_memory.c | 8 ++++++++
> mm/page_alloc.c | 2 ++
> mm/vmstat.c | 1 +
> 7 files changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> index 66cad5c..851ddfd 100644
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -895,6 +895,7 @@ HardwareCorrupted: 0 kB
> AnonHugePages: 49152 kB
> ShmemHugePages: 0 kB
> ShmemPmdMapped: 0 kB
> +LazyFreePages: 0 kB
>
>
> MemTotal: Total usable ram (i.e. physical ram minus a few reserved
> @@ -902,12 +903,13 @@ ShmemPmdMapped: 0 kB
> MemFree: The sum of LowFree+HighFree
> MemAvailable: An estimate of how much memory is available for starting new
> applications, without swapping. Calculated from MemFree,
> - SReclaimable, the size of the file LRU lists, and the low
> - watermarks in each zone.
> + SReclaimable, the size of the file LRU lists, LazyFree pages
> + and the low watermarks in each zone.
> The estimate takes into account that the system needs some
> page cache to function well, and that not all reclaimable
> - slab will be reclaimable, due to items being in use. The
> - impact of those factors will vary from system to system.
> + slab and LazyFree pages will be reclaimable, due to items
> + being in use. The impact of those factors will vary from
> + system to system.
> Buffers: Relatively temporary storage for raw disk blocks
> shouldn't get tremendously large (20MB or so)
> Cached: in-memory cache for files read from the disk (the
> @@ -945,6 +947,8 @@ AnonHugePages: Non-file backed huge pages mapped into userspace page tables
> ShmemHugePages: Memory used by shared memory (shmem) and tmpfs allocated
> with huge pages
> ShmemPmdMapped: Shared memory mapped into userspace with huge pages
> +LazyFreePages: Cleanly freeable pages under memory pressure (i.e. deferred
> + split THP).
> KReclaimable: Kernel allocations that the kernel will attempt to reclaim
> under memory pressure. Includes SReclaimable (below), and other
> direct allocations with a shrinker.
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 8598fcb..ef701aa 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -427,6 +427,7 @@ static ssize_t node_read_meminfo(struct device *dev,
> "Node %d ShmemHugePages: %8lu kB\n"
> "Node %d ShmemPmdMapped: %8lu kB\n"
> #endif
> + "Node %d LazyFreePages: %8lu kB\n"
> ,
> nid, K(node_page_state(pgdat, NR_FILE_DIRTY)),
> nid, K(node_page_state(pgdat, NR_WRITEBACK)),
> @@ -453,6 +454,8 @@ static ssize_t node_read_meminfo(struct device *dev,
> nid, K(node_page_state(pgdat, NR_SHMEM_PMDMAPPED) *
> HPAGE_PMD_NR)
> #endif
> + ,
> + nid, K(node_page_state(pgdat, NR_LAZYFREE))
> );
> n += hugetlb_report_node_meminfo(nid, buf + n);
> return n;
> diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> index 568d90e..b02ebd0 100644
> --- a/fs/proc/meminfo.c
> +++ b/fs/proc/meminfo.c
> @@ -138,6 +138,9 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
> global_node_page_state(NR_SHMEM_PMDMAPPED) * HPAGE_PMD_NR);
> #endif
>
> + show_val_kb(m, "LazyFreePages: ",
> + global_node_page_state(NR_LAZYFREE));
> +
> #ifdef CONFIG_CMA
> show_val_kb(m, "CmaTotal: ", totalcma_pages);
> show_val_kb(m, "CmaFree: ",
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 7799166..523ea86 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -235,6 +235,7 @@ enum node_stat_item {
> NR_SHMEM_THPS,
> NR_SHMEM_PMDMAPPED,
> NR_ANON_THPS,
> + NR_LAZYFREE, /* Lazyfree pages, i.e. deferred split THP */
> NR_UNSTABLE_NFS, /* NFS unstable pages */
> NR_VMSCAN_WRITE,
> NR_VMSCAN_IMMEDIATE, /* Prioritise for reclaim when writeback ends */
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 4f20273..78806c7 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2757,6 +2757,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
> if (!list_empty(page_deferred_list(head))) {
> ds_queue->split_queue_len--;
> list_del(page_deferred_list(head));
> + __mod_node_page_state(NODE_DATA(page_to_nid(head)),
> + NR_LAZYFREE, -HPAGE_PMD_NR);
> }
> if (mapping)
> __dec_node_page_state(page, NR_SHMEM_THPS);
> @@ -2806,6 +2808,8 @@ void free_transhuge_page(struct page *page)
> if (!list_empty(page_deferred_list(page))) {
> ds_queue->split_queue_len--;
> list_del(page_deferred_list(page));
> + __mod_node_page_state(NODE_DATA(page_to_nid(page)),
> + NR_LAZYFREE, -HPAGE_PMD_NR);
> }
> spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
> free_compound_page(page);
> @@ -2822,6 +2826,8 @@ void deferred_split_huge_page(struct page *page)
> spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
> if (list_empty(page_deferred_list(page))) {
> count_vm_event(THP_DEFERRED_SPLIT_PAGE);
> + __mod_node_page_state(NODE_DATA(page_to_nid(page)),
> + NR_LAZYFREE, HPAGE_PMD_NR);
> list_add_tail(page_deferred_list(page), &ds_queue->split_queue);
> ds_queue->split_queue_len++;
> if (memcg)
> @@ -2873,6 +2879,8 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
> /* We lost race with put_compound_page() */
> list_del_init(page_deferred_list(page));
> ds_queue->split_queue_len--;
> + __mod_node_page_state(NODE_DATA(page_to_nid(page)),
> + NR_LAZYFREE, -HPAGE_PMD_NR);
> }
> if (!--sc->nr_to_scan)
> break;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7f27f4e..cab50e8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5210,6 +5210,7 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask)
> " shmem_pmdmapped: %lukB"
> " anon_thp: %lukB"
> #endif
> + " lazyfree:%lukB"
> " writeback_tmp:%lukB"
> " unstable:%lukB"
> " all_unreclaimable? %s"
> @@ -5232,6 +5233,7 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask)
> * HPAGE_PMD_NR),
> K(node_page_state(pgdat, NR_ANON_THPS) * HPAGE_PMD_NR),
> #endif
> + K(node_page_state(pgdat, NR_LAZYFREE)),
> K(node_page_state(pgdat, NR_WRITEBACK_TEMP)),
> K(node_page_state(pgdat, NR_UNSTABLE_NFS)),
> pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES ?
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index a7d4933..87703f2 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1158,6 +1158,7 @@ int fragmentation_index(struct zone *zone, unsigned int order)
> "nr_shmem_hugepages",
> "nr_shmem_pmdmapped",
> "nr_anon_transparent_hugepages",
> + "nr_lazyfree",
> "nr_unstable",
> "nr_vmscan_write",
> "nr_vmscan_immediate_reclaim",
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