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SubjectRe: [PATCH 1/2] zsmalloc: add function to query object size
On 11/28/2012 11:45 PM, Minchan Kim wrote:
> On Mon, Nov 26, 2012 at 11:26:40PM -0800, Nitin Gupta wrote:
>> Adds zs_get_object_size(handle) which provides the size of
>> the given object. This is useful since the user (zram etc.)
>> now do not have to maintain object sizes separately, saving
>> on some metadata size (4b per page).
>>
>> The object handle encodes <page, offset> pair which currently points
>
> Nitpick.
>
> <page, index> in descrption would be proper instead of
> <page, offset>. You are going to replace <page, idx> with <page, offset>.
>

I think 'offset' conveys the meaning more clearly; 'index' is after all
just a chopped-off version of offset :)


>> to the start of the object. Now, the handle implicitly stores the size
>> information by pointing to the object's end instead. Since zsmalloc is
>> a slab based allocator, the start of the object can be easily determined
>> and the difference between the end offset encoded in the handle and the
>> start gives us the object size.
>
> It's a good idea. Look at just minor comment below.
>
> Let's talk with another concern. This patch surely helps current
> customer's memory usage who should add 4 byte for accounting the
> statistics while zsmalloc could be slow down.
> Is it really valuable?
>
> Yes. zram/zcache had a tight coupling with zsmalloc so it already
> lost modularity. :( In this POV, this patch makes sense.
> But if someone are willing to remove statistics for performance?
> Although he remove it, zsmalloc is still slow down.
>
> Statistic for user of zsmalloc should be cost of user himself, not zsmalloc
> and it accelerates dependency with customer so it makes changing allocator
> hard in future. We already had such experience(xvmalloc->zsmalloc). Of course,
> it's not good that worry future things too early without any plan.
> So I'm not strong againt you. If any reviewer don't raise an eyebrow,
> I wil rely on your decision.
>

Looking over the changes I do not expect any difference in performance
-- just a bit more arithmetic, however the use of get_prev_page() which
may dereference a few extra pointers might not be really free. Also, my
iozone test[1] shows very little difference in performance:

With just the fix for crash (patch 1/2):
9.28user 1159.84system 21:46.54elapsed 89%CPU (0avgtext+0avgdata
50200maxresident)k
212988544inputs+190660816outputs (1major+16706minor)pagefaults 0swaps

With the new get_object_size() code (patch 1/2 + patch 2/2):
9.20user 1112.63system 21:03.61elapsed 88%CPU (0avgtext+0avgdata
50200maxresident)k
194636568inputs+190500424outputs (1major+16707minor)pagefaults 0swaps

I really cannot explain this ~40s speedup but anyways, I think
optimizing zsmalloc/zram should be taken up separately, at least when
this new code does not seem to have any significant effects.


[1] iozone test:
- Create zram of size 1200m
- Create ext4 fs
- iozone -a -g 1G
- In parallel: watch zram_stress

# zram_stress
sync
echo 1 | sudo tee /proc/sys/vm/drop_caches


Surely, not the most accurate of the tests but gives an idea if anything
is making a significant difference.

Thanks,
Nitin


>
>>
>> Signed-off-by: Nitin Gupta <ngupta@vflare.org>
>> ---
>> drivers/staging/zsmalloc/zsmalloc-main.c | 177 +++++++++++++++++++++---------
>> drivers/staging/zsmalloc/zsmalloc.h | 1 +
>> 2 files changed, 127 insertions(+), 51 deletions(-)
>>
>> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c
>> index 09a9d35..65c9d3b 100644
>> --- a/drivers/staging/zsmalloc/zsmalloc-main.c
>> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c
>> @@ -112,20 +112,20 @@
>> #define MAX_PHYSMEM_BITS 36
>> #else /* !CONFIG_HIGHMEM64G */
>> /*
>> - * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just
>> + * If this definition of MAX_PHYSMEM_BITS is used, OFFSET_BITS will just
>> * be PAGE_SHIFT
>> */
>> #define MAX_PHYSMEM_BITS BITS_PER_LONG
>> #endif
>> #endif
>> #define _PFN_BITS (MAX_PHYSMEM_BITS - PAGE_SHIFT)
>> -#define OBJ_INDEX_BITS (BITS_PER_LONG - _PFN_BITS)
>> -#define OBJ_INDEX_MASK ((_AC(1, UL) << OBJ_INDEX_BITS) - 1)
>> +#define OFFSET_BITS (BITS_PER_LONG - _PFN_BITS)
>> +#define OFFSET_MASK ((_AC(1, UL) << OFFSET_BITS) - 1)
>>
>> #define MAX(a, b) ((a) >= (b) ? (a) : (b))
>> /* ZS_MIN_ALLOC_SIZE must be multiple of ZS_ALIGN */
>> #define ZS_MIN_ALLOC_SIZE \
>> - MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
>> + MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OFFSET_BITS))
>> #define ZS_MAX_ALLOC_SIZE PAGE_SIZE
>>
>> /*
>> @@ -256,6 +256,11 @@ static int is_last_page(struct page *page)
>> return PagePrivate2(page);
>> }
>>
>> +static unsigned long get_page_index(struct page *page)
>
> IMO, first_obj_offset(struct page *page) would be better readable.
>
>> +{
>> + return is_first_page(page) ? 0 : page->index;
>> +}
>> +
>> static void get_zspage_mapping(struct page *page, unsigned int *class_idx,
>> enum fullness_group *fullness)
>> {
>> @@ -433,39 +438,86 @@ static struct page *get_next_page(struct page *page)
>> return next;
>> }
>>
>> -/* Encode <page, obj_idx> as a single handle value */
>> -static void *obj_location_to_handle(struct page *page, unsigned long obj_idx)
>> +static struct page *get_prev_page(struct page *page)
>> {
>> - unsigned long handle;
>> + struct page *prev, *first_page;
>>
>> - if (!page) {
>> - BUG_ON(obj_idx);
>> - return NULL;
>> - }
>> + first_page = get_first_page(page);
>> + if (page == first_page)
>> + prev = NULL;
>> + else if (page == (struct page *)first_page->private)
>> + prev = first_page;
>> + else
>> + prev = list_entry(page->lru.prev, struct page, lru);
>>
>> - handle = page_to_pfn(page) << OBJ_INDEX_BITS;
>> - handle |= (obj_idx & OBJ_INDEX_MASK);
>> + return prev;
>>
>> - return (void *)handle;
>> }
>>
>> -/* Decode <page, obj_idx> pair from the given object handle */
>> -static void obj_handle_to_location(unsigned long handle, struct page **page,
>> - unsigned long *obj_idx)
>> +static void *encode_ptr(struct page *page, unsigned long offset)
>> {
>> - *page = pfn_to_page(handle >> OBJ_INDEX_BITS);
>> - *obj_idx = handle & OBJ_INDEX_MASK;
>> + unsigned long ptr;
>> + ptr = page_to_pfn(page) << OFFSET_BITS;
>> + ptr |= offset & OFFSET_MASK;
>> + return (void *)ptr;
>> +}
>> +
>> +static void decode_ptr(unsigned long ptr, struct page **page,
>> + unsigned int *offset)
>> +{
>> + *page = pfn_to_page(ptr >> OFFSET_BITS);
>> + *offset = ptr & OFFSET_MASK;
>> +}
>> +
>> +static struct page *obj_handle_to_page(unsigned long handle)
>> +{
>> + struct page *page;
>> + unsigned int offset;
>> +
>> + decode_ptr(handle, &page, &offset);
>> + if (offset < get_page_index(page))
>> + page = get_prev_page(page);
>> +
>> + return page;
>> +}
>> +
>> +static unsigned int obj_handle_to_offset(unsigned long handle,
>> + unsigned int class_size)
>> +{
>> + struct page *page;
>> + unsigned int offset;
>> +
>> + decode_ptr(handle, &page, &offset);
>> + if (offset < get_page_index(page))
>> + offset = PAGE_SIZE - class_size + get_page_index(page);
>
> Althoug it's trivial, we can reduce get_page_index calling.
>
>> + else
>> + offset = roundup(offset, class_size) - class_size;
>> +
>> + return offset;
>> }
>>
>> -static unsigned long obj_idx_to_offset(struct page *page,
>> - unsigned long obj_idx, int class_size)
>> +/* Encode <page, offset, size> as a single handle value */
>
> Need more kind comment about encoding scheme with obj's end <page, offset>
>
>> +static void *obj_location_to_handle(struct page *page, unsigned int offset,
>> + unsigned int size, unsigned int class_size)
>> {
>> - unsigned long off = 0;
>> + struct page *endpage;
>> + unsigned int endoffset;
>>
>> - if (!is_first_page(page))
>> - off = page->index;
>> + if (!page) {
>> + BUG_ON(offset);
>> + return NULL;
>> + }
>
> What do you expect to catch with above check?
>
>> + BUG_ON(offset >= PAGE_SIZE);
>> +
>> + endpage = page;
>> + endoffset = offset + size - 1;
>> + if (endoffset >= PAGE_SIZE) {
>> + endpage = get_next_page(page);
>> + BUG_ON(!endpage);
>> + endoffset -= PAGE_SIZE;
>> + }
>>
>> - return off + obj_idx * class_size;
>> + return encode_ptr(endpage, endoffset);
>> }
>>
>> static void reset_page(struct page *page)
>> @@ -506,14 +558,13 @@ static void free_zspage(struct page *first_page)
>> /* Initialize a newly allocated zspage */
>> static void init_zspage(struct page *first_page, struct size_class *class)
>> {
>> - unsigned long off = 0;
>> + unsigned long off = 0, next_off = 0;
>> struct page *page = first_page;
>>
>> BUG_ON(!is_first_page(first_page));
>> while (page) {
>> struct page *next_page;
>> struct link_free *link;
>> - unsigned int i, objs_on_page;
>>
>> /*
>> * page->index stores offset of first object starting
>> @@ -526,14 +577,12 @@ static void init_zspage(struct page *first_page, struct size_class *class)
>>
>> link = (struct link_free *)kmap_atomic(page) +
>> off / sizeof(*link);
>> - objs_on_page = (PAGE_SIZE - off) / class->size;
>>
>> - for (i = 1; i <= objs_on_page; i++) {
>> - off += class->size;
>> - if (off < PAGE_SIZE) {
>> - link->next = obj_location_to_handle(page, i);
>> - link += class->size / sizeof(*link);
>> - }
>> + next_off = off + class->size;
>> + while (next_off < PAGE_SIZE) {
>> + link->next = encode_ptr(page, next_off);
>> + link += class->size / sizeof(*link);
>> + next_off += class->size;
>> }
>>
>> /*
>> @@ -542,10 +591,11 @@ static void init_zspage(struct page *first_page, struct size_class *class)
>> * page (if present)
>> */
>> next_page = get_next_page(page);
>> - link->next = obj_location_to_handle(next_page, 0);
>> + next_off = next_page ? next_off - PAGE_SIZE : 0;
>> + link->next = encode_ptr(next_page, next_off);
>> kunmap_atomic(link);
>> page = next_page;
>> - off = (off + class->size) % PAGE_SIZE;
>> + off = next_off;
>> }
>> }
>>
>> @@ -596,7 +646,7 @@ static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
>>
>> init_zspage(first_page, class);
>>
>> - first_page->freelist = obj_location_to_handle(first_page, 0);
>> + first_page->freelist = encode_ptr(first_page, 0);
>> /* Maximum number of objects we can store in this zspage */
>> first_page->objects = class->pages_per_zspage * PAGE_SIZE / class->size;
>>
>> @@ -871,7 +921,7 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
>> struct size_class *class;
>>
>> struct page *first_page, *m_page;
>> - unsigned long m_objidx, m_offset;
>> + unsigned int m_offset;
>>
>> if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
>> return 0;
>> @@ -895,8 +945,7 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
>> }
>>
>> obj = (unsigned long)first_page->freelist;
>> - obj_handle_to_location(obj, &m_page, &m_objidx);
>> - m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);
>> + decode_ptr(obj, &m_page, &m_offset);
>>
>> link = (struct link_free *)kmap_atomic(m_page) +
>> m_offset / sizeof(*link);
>> @@ -907,6 +956,9 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
>> first_page->inuse++;
>> /* Now move the zspage to another fullness group, if required */
>> fix_fullness_group(pool, first_page);
>> +
>> + obj = (unsigned long)obj_location_to_handle(m_page, m_offset,
>> + size, class->size);
>> spin_unlock(&class->lock);
>>
>> return obj;
>> @@ -917,7 +969,7 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
>> {
>> struct link_free *link;
>> struct page *first_page, *f_page;
>> - unsigned long f_objidx, f_offset;
>> + unsigned long f_offset;
>>
>> int class_idx;
>> struct size_class *class;
>> @@ -926,12 +978,12 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
>> if (unlikely(!obj))
>> return;
>>
>> - obj_handle_to_location(obj, &f_page, &f_objidx);
>> + f_page = obj_handle_to_page(obj);
>> first_page = get_first_page(f_page);
>>
>> get_zspage_mapping(first_page, &class_idx, &fullness);
>> class = &pool->size_class[class_idx];
>> - f_offset = obj_idx_to_offset(f_page, f_objidx, class->size);
>> + f_offset = obj_handle_to_offset(obj, class->size);
>>
>> spin_lock(&class->lock);
>>
>> @@ -940,7 +992,7 @@ void zs_free(struct zs_pool *pool, unsigned long obj)
>> + f_offset);
>> link->next = first_page->freelist;
>> kunmap_atomic(link);
>> - first_page->freelist = (void *)obj;
>> + first_page->freelist = encode_ptr(f_page, f_offset);
>>
>> first_page->inuse--;
>> fullness = fix_fullness_group(pool, first_page);
>> @@ -970,10 +1022,10 @@ EXPORT_SYMBOL_GPL(zs_free);
>> * This function returns with preemption and page faults disabled.
>> */
>> void *zs_map_object(struct zs_pool *pool, unsigned long handle,
>> - enum zs_mapmode mm)
>> + enum zs_mapmode mm)
>> {
>> struct page *page;
>> - unsigned long obj_idx, off;
>> + unsigned long off;
>>
>> unsigned int class_idx;
>> enum fullness_group fg;
>> @@ -990,10 +1042,10 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
>> */
>> BUG_ON(in_interrupt());
>>
>> - obj_handle_to_location(handle, &page, &obj_idx);
>> + page = obj_handle_to_page(handle);
>> get_zspage_mapping(get_first_page(page), &class_idx, &fg);
>> class = &pool->size_class[class_idx];
>> - off = obj_idx_to_offset(page, obj_idx, class->size);
>> + off = obj_handle_to_offset(handle, class->size);
>>
>> area = &get_cpu_var(zs_map_area);
>> area->vm_mm = mm;
>> @@ -1015,7 +1067,7 @@ EXPORT_SYMBOL_GPL(zs_map_object);
>> void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>> {
>> struct page *page;
>> - unsigned long obj_idx, off;
>> + unsigned long off;
>>
>> unsigned int class_idx;
>> enum fullness_group fg;
>> @@ -1024,10 +1076,10 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>>
>> BUG_ON(!handle);
>>
>> - obj_handle_to_location(handle, &page, &obj_idx);
>> + page = obj_handle_to_page(handle);
>> get_zspage_mapping(get_first_page(page), &class_idx, &fg);
>> class = &pool->size_class[class_idx];
>> - off = obj_idx_to_offset(page, obj_idx, class->size);
>> + off = obj_handle_to_offset(handle, class->size);
>>
>> area = &__get_cpu_var(zs_map_area);
>> if (off + class->size <= PAGE_SIZE)
>> @@ -1045,6 +1097,29 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>> }
>> EXPORT_SYMBOL_GPL(zs_unmap_object);
>>
>> +size_t zs_get_object_size(struct zs_pool *pool, unsigned long handle)
>> +{
>> + struct page *endpage;
>> + unsigned int endoffset, size;
>> +
>> + unsigned int class_idx;
>> + enum fullness_group fg;
>> + struct size_class *class;
>> +
>> + decode_ptr(handle, &endpage, &endoffset);
>> + get_zspage_mapping(endpage, &class_idx, &fg);
>> + class = &pool->size_class[class_idx];
>> +
>> + size = endoffset + 1;
>> + if (endoffset < get_page_index(endpage))
>> + size += class->size - get_page_index(endpage);
>> + else
>> + size -= rounddown(endoffset, class->size);
>> +
>> + return size;
>> +}
>> +EXPORT_SYMBOL_GPL(zs_get_object_size);
>> +
>> u64 zs_get_total_size_bytes(struct zs_pool *pool)
>> {
>> int i;
>> diff --git a/drivers/staging/zsmalloc/zsmalloc.h b/drivers/staging/zsmalloc/zsmalloc.h
>> index de2e8bf..2830fdf 100644
>> --- a/drivers/staging/zsmalloc/zsmalloc.h
>> +++ b/drivers/staging/zsmalloc/zsmalloc.h
>> @@ -38,6 +38,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
>> enum zs_mapmode mm);
>> void zs_unmap_object(struct zs_pool *pool, unsigned long handle);
>>
>> +size_t zs_get_object_size(struct zs_pool *pool, unsigned long handle);
>> u64 zs_get_total_size_bytes(struct zs_pool *pool);
>>
>> #endif
>> --
>> 1.7.10.4
>>
>> --
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>



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