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Date: Wed, 11 Jan 2017 11:24:26 -0500
From: Dan Streetman <ddstreet@...e.org>
To: Vitaly Wool <vitalywool@...il.com>
Cc: Linux-MM <linux-mm@...ck.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH/RESEND v2 2/5] z3fold: fix header size related issues
On Wed, Jan 11, 2017 at 10:06 AM, Vitaly Wool <vitalywool@...il.com> wrote:
> Currently the whole kernel build will be stopped if the size of struct
> z3fold_header is greater than the size of one chunk, which is 64 bytes by
> default. This patch instead defines the offset for z3fold objects as the
> size of the z3fold header in chunks.
>
> Fixed also are the calculation of num_free_chunks() and the address to
> move the middle chunk to in case of in-page compaction in
> z3fold_compact_page().
>
> Signed-off-by: Vitaly Wool <vitalywool@...il.com>
Acked-by: Dan Streetman <ddstreet@...e.org>
> ---
> mm/z3fold.c | 114 ++++++++++++++++++++++++++++++++++--------------------------
> 1 file changed, 64 insertions(+), 50 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 2273789..98ab01f 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -34,29 +34,58 @@
> /*****************
> * Structures
> *****************/
> +struct z3fold_pool;
> +struct z3fold_ops {
> + int (*evict)(struct z3fold_pool *pool, unsigned long handle);
> +};
> +
> +enum buddy {
> + HEADLESS = 0,
> + FIRST,
> + MIDDLE,
> + LAST,
> + BUDDIES_MAX
> +};
> +
> +/*
> + * struct z3fold_header - z3fold page metadata occupying the first chunk of each
> + * z3fold page, except for HEADLESS pages
> + * @buddy: links the z3fold page into the relevant list in the pool
> + * @first_chunks: the size of the first buddy in chunks, 0 if free
> + * @middle_chunks: the size of the middle buddy in chunks, 0 if free
> + * @last_chunks: the size of the last buddy in chunks, 0 if free
> + * @first_num: the starting number (for the first handle)
> + */
> +struct z3fold_header {
> + struct list_head buddy;
> + unsigned short first_chunks;
> + unsigned short middle_chunks;
> + unsigned short last_chunks;
> + unsigned short start_middle;
> + unsigned short first_num:2;
> +};
> +
> /*
> * NCHUNKS_ORDER determines the internal allocation granularity, effectively
> * adjusting internal fragmentation. It also determines the number of
> * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the
> - * allocation granularity will be in chunks of size PAGE_SIZE/64. As one chunk
> - * in allocated page is occupied by z3fold header, NCHUNKS will be calculated
> - * to 63 which shows the max number of free chunks in z3fold page, also there
> - * will be 63 freelists per pool.
> + * allocation granularity will be in chunks of size PAGE_SIZE/64. Some chunks
> + * in the beginning of an allocated page are occupied by z3fold header, so
> + * NCHUNKS will be calculated to 63 (or 62 in case CONFIG_DEBUG_SPINLOCK=y),
> + * which shows the max number of free chunks in z3fold page, also there will
> + * be 63, or 62, respectively, freelists per pool.
> */
> #define NCHUNKS_ORDER 6
>
> #define CHUNK_SHIFT (PAGE_SHIFT - NCHUNKS_ORDER)
> #define CHUNK_SIZE (1 << CHUNK_SHIFT)
> -#define ZHDR_SIZE_ALIGNED CHUNK_SIZE
> +#define ZHDR_SIZE_ALIGNED round_up(sizeof(struct z3fold_header), CHUNK_SIZE)
> +#define ZHDR_CHUNKS (ZHDR_SIZE_ALIGNED >> CHUNK_SHIFT)
> +#define TOTAL_CHUNKS (PAGE_SIZE >> CHUNK_SHIFT)
> #define NCHUNKS ((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT)
>
> #define BUDDY_MASK (0x3)
>
> -struct z3fold_pool;
> -struct z3fold_ops {
> - int (*evict)(struct z3fold_pool *pool, unsigned long handle);
> -};
> -
> /**
> * struct z3fold_pool - stores metadata for each z3fold pool
> * @lock: protects all pool fields and first|last_chunk fields of any
> @@ -86,32 +115,6 @@ struct z3fold_pool {
> const struct zpool_ops *zpool_ops;
> };
>
> -enum buddy {
> - HEADLESS = 0,
> - FIRST,
> - MIDDLE,
> - LAST,
> - BUDDIES_MAX
> -};
> -
> -/*
> - * struct z3fold_header - z3fold page metadata occupying the first chunk of each
> - * z3fold page, except for HEADLESS pages
> - * @buddy: links the z3fold page into the relevant list in the pool
> - * @first_chunks: the size of the first buddy in chunks, 0 if free
> - * @middle_chunks: the size of the middle buddy in chunks, 0 if free
> - * @last_chunks: the size of the last buddy in chunks, 0 if free
> - * @first_num: the starting number (for the first handle)
> - */
> -struct z3fold_header {
> - struct list_head buddy;
> - unsigned short first_chunks;
> - unsigned short middle_chunks;
> - unsigned short last_chunks;
> - unsigned short start_middle;
> - unsigned short first_num:2;
> -};
> -
> /*
> * Internal z3fold page flags
> */
> @@ -121,6 +124,7 @@ enum z3fold_page_flags {
> MIDDLE_CHUNK_MAPPED,
> };
>
> +
> /*****************
> * Helpers
> *****************/
> @@ -204,9 +208,10 @@ static int num_free_chunks(struct z3fold_header *zhdr)
> */
> if (zhdr->middle_chunks != 0) {
> int nfree_before = zhdr->first_chunks ?
> - 0 : zhdr->start_middle - 1;
> + 0 : zhdr->start_middle - ZHDR_CHUNKS;
> int nfree_after = zhdr->last_chunks ?
> - 0 : NCHUNKS - zhdr->start_middle - zhdr->middle_chunks;
> + 0 : TOTAL_CHUNKS -
> + (zhdr->start_middle + zhdr->middle_chunks);
> nfree = max(nfree_before, nfree_after);
> } else
> nfree = NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
> @@ -254,26 +259,35 @@ static void z3fold_destroy_pool(struct z3fold_pool *pool)
> kfree(pool);
> }
>
> +static inline void *mchunk_memmove(struct z3fold_header *zhdr,
> + unsigned short dst_chunk)
> +{
> + void *beg = zhdr;
> + return memmove(beg + (dst_chunk << CHUNK_SHIFT),
> + beg + (zhdr->start_middle << CHUNK_SHIFT),
> + zhdr->middle_chunks << CHUNK_SHIFT);
> +}
> +
> /* Has to be called with lock held */
> static int z3fold_compact_page(struct z3fold_header *zhdr)
> {
> struct page *page = virt_to_page(zhdr);
> - void *beg = zhdr;
>
> + if (test_bit(MIDDLE_CHUNK_MAPPED, &page->private))
> + return 0; /* can't move middle chunk, it's used */
>
> - if (!test_bit(MIDDLE_CHUNK_MAPPED, &page->private) &&
> - zhdr->middle_chunks != 0 &&
> - zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
> - memmove(beg + ZHDR_SIZE_ALIGNED,
> - beg + (zhdr->start_middle << CHUNK_SHIFT),
> - zhdr->middle_chunks << CHUNK_SHIFT);
> + if (zhdr->middle_chunks == 0)
> + return 0; /* nothing to compact */
> +
> + if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
> + /* move to the beginning */
> + mchunk_memmove(zhdr, ZHDR_CHUNKS);
> zhdr->first_chunks = zhdr->middle_chunks;
> zhdr->middle_chunks = 0;
> zhdr->start_middle = 0;
> zhdr->first_num++;
> - return 1;
> }
> - return 0;
> + return 1;
> }
>
> /**
> @@ -365,7 +379,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
> zhdr->last_chunks = chunks;
> else {
> zhdr->middle_chunks = chunks;
> - zhdr->start_middle = zhdr->first_chunks + 1;
> + zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
> }
>
> if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
> @@ -778,8 +792,8 @@ MODULE_ALIAS("zpool-z3fold");
>
> static int __init init_z3fold(void)
> {
> - /* Make sure the z3fold header will fit in one chunk */
> - BUILD_BUG_ON(sizeof(struct z3fold_header) > ZHDR_SIZE_ALIGNED);
> + /* Make sure the z3fold header is not larger than the page size */
> + BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE);
> zpool_register_driver(&z3fold_zpool_driver);
>
> return 0;
> --
> 2.4.2
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