| Message ID | 1488432825-92126-5-git-send-email-pasha.tatashin@oracle.com |
|---|---|
| State | Not Applicable |
| Delegated to: | David Miller |
| Headers | show |
On Thu, 2 Mar 2017 00:33:45 -0500 Pavel Tatashin <pasha.tatashin@oracle.com> wrote: > Allow hash tables to scale with memory but at slower pace, when HASH_ADAPT > is provided every time memory quadruples the sizes of hash tables will only > double instead of quadrupling as well. This algorithm starts working only > when memory size reaches a certain point, currently set to 64G. > > This is example of dentry hash table size, before and after four various > memory configurations: > > MEMORY SCALE HASH_SIZE > old new old new > 8G 13 13 8M 8M > 16G 13 13 16M 16M > 32G 13 13 32M 32M > 64G 13 13 64M 64M > 128G 13 14 128M 64M > 256G 13 14 256M 128M > 512G 13 15 512M 128M > 1024G 13 15 1024M 256M > 2048G 13 16 2048M 256M > 4096G 13 16 4096M 512M > 8192G 13 17 8192M 512M > 16384G 13 17 16384M 1024M > 32768G 13 18 32768M 1024M > 65536G 13 18 65536M 2048M OK, but what are the runtime effects? Presumably some workloads will slow down a bit. How much? How do we know that this is a worthwhile tradeoff? If the effect of this change is "undetectable" then those hash tables are simply too large, and additional tuning is needed, yes? -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 03/03/2017 06:32 PM, Andrew Morton wrote: > On Thu, 2 Mar 2017 00:33:45 -0500 Pavel Tatashin <pasha.tatashin@oracle.com> wrote: > >> Allow hash tables to scale with memory but at slower pace, when HASH_ADAPT >> is provided every time memory quadruples the sizes of hash tables will only >> double instead of quadrupling as well. This algorithm starts working only >> when memory size reaches a certain point, currently set to 64G. >> >> This is example of dentry hash table size, before and after four various >> memory configurations: >> >> MEMORY SCALE HASH_SIZE >> old new old new >> 8G 13 13 8M 8M >> 16G 13 13 16M 16M >> 32G 13 13 32M 32M >> 64G 13 13 64M 64M >> 128G 13 14 128M 64M >> 256G 13 14 256M 128M >> 512G 13 15 512M 128M >> 1024G 13 15 1024M 256M >> 2048G 13 16 2048M 256M >> 4096G 13 16 4096M 512M >> 8192G 13 17 8192M 512M >> 16384G 13 17 16384M 1024M >> 32768G 13 18 32768M 1024M >> 65536G 13 18 65536M 2048M > > OK, but what are the runtime effects? Presumably some workloads will > slow down a bit. How much? How do we know that this is a worthwhile > tradeoff? > > If the effect of this change is "undetectable" then those hash tables > are simply too large, and additional tuning is needed, yes? > Hi Andrew, The effect of this change on runtime is undetectable as filesystem growth is not proportional to machine memory size as what is currently assumed. The change effects only large memory machine. Additional tuning might be needed, but that can be done by the clients of the kmem_cache_create interface, not the generic cache allocator itself. Thank you, Pasha -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/dcache.c b/fs/dcache.c index 363502f..808ea99 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -3585,7 +3585,7 @@ static void __init dcache_init(void) sizeof(struct hlist_bl_head), dhash_entries, 13, - HASH_ZERO, + HASH_ZERO | HASH_ADAPT, &d_hash_shift, &d_hash_mask, 0, diff --git a/fs/inode.c b/fs/inode.c index 1b15a7c..32c8ee4 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -1953,7 +1953,7 @@ void __init inode_init(void) sizeof(struct hlist_head), ihash_entries, 14, - HASH_ZERO, + HASH_ZERO | HASH_ADAPT, &i_hash_shift, &i_hash_mask, 0, diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h index e223d91..dbaf312 100644 --- a/include/linux/bootmem.h +++ b/include/linux/bootmem.h @@ -359,6 +359,7 @@ static inline void __init memblock_free_late( #define HASH_SMALL 0x00000002 /* sub-page allocation allowed, min * shift passed via *_hash_shift */ #define HASH_ZERO 0x00000004 /* Zero allocated hash table */ +#define HASH_ADAPT 0x00000008 /* Adaptive scale for large memory */ /* Only NUMA needs hash distribution. 64bit NUMA architectures have * sufficient vmalloc space. diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 1b0f7a4..608055e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -7124,6 +7124,17 @@ static unsigned long __init arch_reserved_kernel_pages(void) #endif /* + * Adaptive scale is meant to reduce sizes of hash tables on large memory + * machines. As memory size is increased the scale is also increased but at + * slower pace. Starting from ADAPT_SCALE_BASE (64G), every time memory + * quadruples the scale is increased by one, which means the size of hash table + * only doubles, instead of quadrupling as well. + */ +#define ADAPT_SCALE_BASE (64ul << 30) +#define ADAPT_SCALE_SHIFT 2 +#define ADAPT_SCALE_NPAGES (ADAPT_SCALE_BASE >> PAGE_SHIFT) + +/* * allocate a large system hash table from bootmem * - it is assumed that the hash table must contain an exact power-of-2 * quantity of entries @@ -7154,6 +7165,14 @@ static unsigned long __init arch_reserved_kernel_pages(void) if (PAGE_SHIFT < 20) numentries = round_up(numentries, (1<<20)/PAGE_SIZE); + if (flags & HASH_ADAPT) { + unsigned long adapt; + + for (adapt = ADAPT_SCALE_NPAGES; adapt < numentries; + adapt <<= ADAPT_SCALE_SHIFT) + scale++; + } + /* limit to 1 bucket per 2^scale bytes of low memory */ if (scale > PAGE_SHIFT) numentries >>= (scale - PAGE_SHIFT);
Allow hash tables to scale with memory but at slower pace, when HASH_ADAPT is provided every time memory quadruples the sizes of hash tables will only double instead of quadrupling as well. This algorithm starts working only when memory size reaches a certain point, currently set to 64G. This is example of dentry hash table size, before and after four various memory configurations: MEMORY SCALE HASH_SIZE old new old new 8G 13 13 8M 8M 16G 13 13 16M 16M 32G 13 13 32M 32M 64G 13 13 64M 64M 128G 13 14 128M 64M 256G 13 14 256M 128M 512G 13 15 512M 128M 1024G 13 15 1024M 256M 2048G 13 16 2048M 256M 4096G 13 16 4096M 512M 8192G 13 17 8192M 512M 16384G 13 17 16384M 1024M 32768G 13 18 32768M 1024M 65536G 13 18 65536M 2048M Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com> --- fs/dcache.c | 2 +- fs/inode.c | 2 +- include/linux/bootmem.h | 1 + mm/page_alloc.c | 19 +++++++++++++++++++ 4 files changed, 22 insertions(+), 2 deletions(-)