From bece2da8d4475708a01695d1d589676729efc614 Mon Sep 17 00:00:00 2001 From: meganz009 Date: Fri, 28 Apr 2023 19:06:09 +0800 Subject: [PATCH] mm: zero-seek shrinkers commit 4b85afbdacd290c7a22c96df40a6433fdcacb509 upstream. The page cache and most shrinkable slab caches hold data that has been read from disk, but there are some caches that only cache CPU work, such as the dentry and inode caches of procfs and sysfs, as well as the subset of radix tree nodes that track non-resident page cache. Currently, all these are shrunk at the same rate: using DEFAULT_SEEKS for the shrinker's seeks setting tells the reclaim algorithm that for every two page cache pages scanned it should scan one slab object. This is a bogus setting. A virtual inode that required no IO to create is not twice as valuable as a page cache page; shadow cache entries with eviction distances beyond the size of memory aren't either. In most cases, the behavior in practice is still fine. Such virtual caches don't tend to grow and assert themselves aggressively, and usually get picked up before they cause problems. But there are scenarios where that's not true. Our database workloads suffer from two of those. For one, their file workingset is several times bigger than available memory, which has the kernel aggressively create shadow page cache entries for the non-resident parts of it. The workingset code does tell the VM that most of these are expendable, but the VM ends up balancing them 2:1 to cache pages as per the seeks setting. This is a huge waste of memory. These workloads also deal with tens of thousands of open files and use /proc for introspection, which ends up growing the proc_inode_cache to absurdly large sizes - again at the cost of valuable cache space, which isn't a reasonable trade-off, given that proc inodes can be re-created without involving the disk. This patch implements a "zero-seek" setting for shrinkers that results in a target ratio of 0:1 between their objects and IO-backed caches. This allows such virtual caches to grow when memory is available (they do cache/avoid CPU work after all), but effectively disables them as soon as IO-backed objects are under pressure. It then switches the shrinkers for procfs and sysfs metadata, as well as excess page cache shadow nodes, to the new zero-seek setting. Link: http://lkml.kernel.org/r/20181009184732.762-5-hannes@cmpxchg.org Signed-off-by: Johannes Weiner Reported-by: Domas Mituzas Reviewed-by: Andrew Morton Reviewed-by: Rik van Riel Acked-by: Peter Zijlstra (Intel) Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/kernfs/mount.c | 3 +++ fs/proc/inode.c | 3 +++ mm/vmscan.c | 15 ++++++++++++--- mm/workingset.c | 2 +- 4 files changed, 19 insertions(+), 4 deletions(-) diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c index b2a126a947e3..c0f1e7e7a883 100644 --- a/fs/kernfs/mount.c +++ b/fs/kernfs/mount.c @@ -240,6 +240,9 @@ static int kernfs_fill_super(struct super_block *sb, unsigned long magic) sb->s_export_op = &kernfs_export_ops; sb->s_time_gran = 1; + /* sysfs dentries and inodes don't require IO to create */ + sb->s_shrink.seeks = 0; + /* get root inode, initialize and unlock it */ mutex_lock(&kernfs_mutex); inode = kernfs_get_inode(sb, info->root->kn); diff --git a/fs/proc/inode.c b/fs/proc/inode.c index 31bf3bb8ddae..93f83b2e85c7 100644 --- a/fs/proc/inode.c +++ b/fs/proc/inode.c @@ -516,6 +516,9 @@ int proc_fill_super(struct super_block *s, void *data, int silent) */ s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH; + /* procfs dentries and inodes don't require IO to create */ + s->s_shrink.seeks = 0; + pde_get(&proc_root); root_inode = proc_get_inode(s, &proc_root); if (!root_inode) { diff --git a/mm/vmscan.c b/mm/vmscan.c index d30f18b2f0a8..ffed599c5753 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -605,9 +605,18 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0); total_scan = nr; - delta = freeable >> priority; - delta *= 4; - do_div(delta, shrinker->seeks); + if (shrinker->seeks) { + delta = freeable >> priority; + delta *= 4; + do_div(delta, shrinker->seeks); + } else { + /* + * These objects don't require any IO to create. Trim + * them aggressively under memory pressure to keep + * them from causing refetches in the IO caches. + */ + delta = freeable / 2; + } total_scan += delta; if (total_scan < 0) { diff --git a/mm/workingset.c b/mm/workingset.c index a2384a5851e8..b51bf88f2482 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -590,7 +590,7 @@ static unsigned long scan_shadow_nodes(struct shrinker *shrinker, static struct shrinker workingset_shadow_shrinker = { .count_objects = count_shadow_nodes, .scan_objects = scan_shadow_nodes, - .seeks = DEFAULT_SEEKS, + .seeks = 0, /* ->count reports only fully expendable nodes */ .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE, }; -- Gitee