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Date: Fri, 30 Nov 2012 22:54:23 +0900
From: Minchan Kim <minchan.kernel.2@...il.com>
To: Nitin Gupta <ngupta@...are.org>
Cc: Greg KH <greg@...ah.com>, Jerome Marchand <jmarchan@...hat.com>,
Seth Jennings <sjenning@...ux.vnet.ibm.com>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Dan Carpenter <dan.carpenter@...cle.com>,
Sam Hansen <solid.se7en@...il.com>,
Linux Driver Project <devel@...uxdriverproject.org>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] zsmalloc: add function to query object size
On Thu, Nov 29, 2012 at 10:54:48PM -0800, Nitin Gupta wrote:
> Changelog v2 vs v1:
> - None
>
> 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
> 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.
>
> Signed-off-by: Nitin Gupta <ngupta@...are.org>
Acked-by: Minchan Kim <minchan@...nel.org>
I already had a few comment in your previous versoin.
I'm OK although you ignore them because I can make follow up patch about
my nitpick but could you answer below my question?
> ---
> 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)
> +{
> + 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);
> + 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 */
> +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?
--
Kind regards,
Minchan Kim
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