Re: [PATCH 1/3] SG: Move functions to lib/scatterlist.c and add sg chaining allocator helpers

Boaz Harrosh
2007-12-20T14:36:56Z

A small comment in body

On Thu, Dec 20 2007 at 16:00 +0200, Boaz Harrosh <bharrosh@panasas.com> wrote:
> Manually doing chained sg lists is not trivial, so add some helpers
> to make sure that drivers get it right.
>
> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
> ---
> include/linux/scatterlist.h | 125 ++++---------------
> lib/Makefile | 2 +-
> lib/scatterlist.c | 281 +++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 307 insertions(+), 101 deletions(-)
> create mode 100644 lib/scatterlist.c
>
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index 416e000..c3ca848 100644
> --- a/include/linux/scatterlist.h
> +++ b/include/linux/scatterlist.h
> @@ -7,6 +7,12 @@
> #include <linux/string.h>
> #include <asm/io.h>
>
> +struct sg_table {
> + struct scatterlist *sgl; /* the list */
> + unsigned int nents; /* number of mapped entries */
> + unsigned int orig_nents; /* original size of list */
> +};
> +
> /*
> * Notes on SG table design.
> *
> @@ -106,31 +112,6 @@ static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
> sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
> }
>
> -/**
> - * sg_next - return the next scatterlist entry in a list
> - * @sg: The current sg entry
> - *
> - * Description:
> - * Usually the next entry will be @sg@ + 1, but if this sg element is part
> - * of a chained scatterlist, it could jump to the start of a new
> - * scatterlist array.
> - *
> - **/
> -static inline struct scatterlist *sg_next(struct scatterlist *sg)
> -{
> -#ifdef CONFIG_DEBUG_SG
> - BUG_ON(sg->sg_magic != SG_MAGIC);
> -#endif
> - if (sg_is_last(sg))
> - return NULL;
> -
> - sg++;
> - if (unlikely(sg_is_chain(sg)))
> - sg = sg_chain_ptr(sg);
> -
> - return sg;
> -}
> -
> /*
> * Loop over each sg element, following the pointer to a new list if necessary
> */
> @@ -138,40 +119,6 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg)
> for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
>
> /**
> - * sg_last - return the last scatterlist entry in a list
> - * @sgl: First entry in the scatterlist
> - * @nents: Number of entries in the scatterlist
> - *
> - * Description:
> - * Should only be used casually, it (currently) scan the entire list
> - * to get the last entry.
> - *
> - * Note that the @sgl@ pointer passed in need not be the first one,
> - * the important bit is that @nents@ denotes the number of entries that
> - * exist from @sgl@.
> - *
> - **/
> -static inline struct scatterlist *sg_last(struct scatterlist *sgl,
> - unsigned int nents)
> -{
> -#ifndef ARCH_HAS_SG_CHAIN
> - struct scatterlist *ret = &sgl[nents - 1];
> -#else
> - struct scatterlist *sg, *ret = NULL;
> - unsigned int i;
> -
> - for_each_sg(sgl, sg, nents, i)
> - ret = sg;
> -
> -#endif
> -#ifdef CONFIG_DEBUG_SG
> - BUG_ON(sgl[0].sg_magic != SG_MAGIC);
> - BUG_ON(!sg_is_last(ret));
> -#endif
> - return ret;
> -}
> -
> -/**
> * sg_chain - Chain two sglists together
> * @prv: First scatterlist
> * @prv_nents: Number of entries in prv
> @@ -223,47 +170,6 @@ static inline void sg_mark_end(struct scatterlist *sg)
> }
>
> /**
> - * sg_init_table - Initialize SG table
> - * @sgl: The SG table
> - * @nents: Number of entries in table
> - *
> - * Notes:
> - * If this is part of a chained sg table, sg_mark_end() should be
> - * used only on the last table part.
> - *
> - **/
> -static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
> -{
> - memset(sgl, 0, sizeof(*sgl) * nents);
> -#ifdef CONFIG_DEBUG_SG
> - {
> - unsigned int i;
> - for (i = 0; i < nents; i++)
> - sgl[i].sg_magic = SG_MAGIC;
> - }
> -#endif
> - sg_mark_end(&sgl[nents - 1]);
> -}
> -
> -/**
> - * sg_init_one - Initialize a single entry sg list
> - * @sg: SG entry
> - * @buf: Virtual address for IO
> - * @buflen: IO length
> - *
> - * Notes:
> - * This should not be used on a single entry that is part of a larger
> - * table. Use sg_init_table() for that.
> - *
> - **/
> -static inline void sg_init_one(struct scatterlist *sg, const void *buf,
> - unsigned int buflen)
> -{
> - sg_init_table(sg, 1);
> - sg_set_buf(sg, buf, buflen);
> -}
> -
> -/**
> * sg_phys - Return physical address of an sg entry
> * @sg: SG entry
> *
> @@ -293,4 +199,23 @@ static inline void *sg_virt(struct scatterlist *sg)
> return page_address(sg_page(sg)) + sg->offset;
> }
>
> +struct scatterlist *sg_next(struct scatterlist *);
I don't like that this became exported. I would prefer if
it could stay inline. if at all possible?

> +struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
> +void sg_init_table(struct scatterlist *, unsigned int);
> +void sg_init_one(struct scatterlist *, const void *, unsigned int);
> +
> +typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t);
> +typedef void (sg_free_fn)(struct scatterlist *, unsigned int);
> +
> +void __sg_free_table(struct sg_table *, sg_free_fn *);
> +void sg_free_table(struct sg_table *);
> +int __sg_alloc_table(struct sg_table *, unsigned int, gfp_t, sg_alloc_fn *);
> +int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
> +
> +/*
> + * Maximum number of entries that will be allocated in one piece, if
> + * a list larger than this is required then chaining will be utilized.
> + */
> +#define SG_MAX_SINGLE_ALLOC (PAGE_SIZE / sizeof(struct scatterlist))
Yes this is a well needed calculation.

Only now the SCSI part of the allocator is missing.
What is needed is the code a posted a while back that
automatically adjusts pools and sizes to this constant.
I will post that again soon.
(Note that this is a bug on current code since above is 256
in 32 bit code and scsi_lib is only ready for 128)

> +
> #endif /* _LINUX_SCATTERLIST_H */
> diff --git a/lib/Makefile b/lib/Makefile
> index b6793ed..89841dc 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -6,7 +6,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
> rbtree.o radix-tree.o dump_stack.o \
> idr.o int_sqrt.o extable.o prio_tree.o \
> sha1.o irq_regs.o reciprocal_div.o argv_split.o \
> - proportions.o prio_heap.o
> + proportions.o prio_heap.o scatterlist.o
>
> lib-$(CONFIG_MMU) += ioremap.o
> lib-$(CONFIG_SMP) += cpumask.o
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> new file mode 100644
> index 0000000..02aaa27
> --- /dev/null
> +++ b/lib/scatterlist.c
> @@ -0,0 +1,281 @@
> +/*
> + * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com>
> + *
> + * Scatterlist handling helpers.
> + *
> + * This source code is licensed under the GNU General Public License,
> + * Version 2. See the file COPYING for more details.
> + */
> +#include <linux/module.h>
> +#include <linux/scatterlist.h>
> +
> +/**
> + * sg_next - return the next scatterlist entry in a list
> + * @sg: The current sg entry
> + *
> + * Description:
> + * Usually the next entry will be @sg@ + 1, but if this sg element is part
> + * of a chained scatterlist, it could jump to the start of a new
> + * scatterlist array.
> + *
> + **/
> +struct scatterlist *sg_next(struct scatterlist *sg)
> +{
> +#ifdef CONFIG_DEBUG_SG
> + BUG_ON(sg->sg_magic != SG_MAGIC);
> +#endif
> + if (sg_is_last(sg))
> + return NULL;
> +
> + sg++;
> + if (unlikely(sg_is_chain(sg)))
> + sg = sg_chain_ptr(sg);
> +
> + return sg;
> +}
> +EXPORT_SYMBOL(sg_next);
> +
> +/**
> + * sg_last - return the last scatterlist entry in a list
> + * @sgl: First entry in the scatterlist
> + * @nents: Number of entries in the scatterlist
> + *
> + * Description:
> + * Should only be used casually, it (currently) scans the entire list
> + * to get the last entry.
> + *
> + * Note that the @sgl@ pointer passed in need not be the first one,
> + * the important bit is that @nents@ denotes the number of entries that
> + * exist from @sgl@.
> + *
> + **/
> +struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
> +{
> +#ifndef ARCH_HAS_SG_CHAIN
> + struct scatterlist *ret = &sgl[nents - 1];
> +#else
> + struct scatterlist *sg, *ret = NULL;
> + unsigned int i;
> +
> + for_each_sg(sgl, sg, nents, i)
> + ret = sg;
> +
> +#endif
> +#ifdef CONFIG_DEBUG_SG
> + BUG_ON(sgl[0].sg_magic != SG_MAGIC);
> + BUG_ON(!sg_is_last(ret));
> +#endif
> + return ret;
> +}
> +EXPORT_SYMBOL(sg_last);
> +
> +/**
> + * sg_init_table - Initialize SG table
> + * @sgl: The SG table
> + * @nents: Number of entries in table
> + *
> + * Notes:
> + * If this is part of a chained sg table, sg_mark_end() should be
> + * used only on the last table part.
> + *
> + **/
> +void sg_init_table(struct scatterlist *sgl, unsigned int nents)
> +{
> + memset(sgl, 0, sizeof(*sgl) * nents);
> +#ifdef CONFIG_DEBUG_SG
> + {
> + unsigned int i;
> + for (i = 0; i < nents; i++)
> + sgl[i].sg_magic = SG_MAGIC;
> + }
> +#endif
> + sg_mark_end(&sgl[nents - 1]);
> +}
> +EXPORT_SYMBOL(sg_init_table);
> +
> +/**
> + * sg_init_one - Initialize a single entry sg list
> + * @sg: SG entry
> + * @buf: Virtual address for IO
> + * @buflen: IO length
> + *
> + **/
> +void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
> +{
> + sg_init_table(sg, 1);
> + sg_set_buf(sg, buf, buflen);
> +}
> +EXPORT_SYMBOL(sg_init_one);
> +
> +/*
> + * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
> + * helpers.
> + */
> +static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
> +{
> + if (nents == SG_MAX_SINGLE_ALLOC)
> + return (struct scatterlist *) __get_free_page(gfp_mask);
> + else
> + return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
> +}
> +
> +static void sg_kfree(struct scatterlist *sg, unsigned int nents)
> +{
> + if (nents == SG_MAX_SINGLE_ALLOC)
> + free_page((unsigned long) sg);
> + else
> + kfree(sg);
> +}
> +
> +/**
> + * __sg_free_table - Free a previously mapped sg table
> + * @table: The sg table header to use
> + * @free_fn: Free function
> + *
> + * Description:
> + * Free an sg table previously allocated and setup with __sg_alloc_table().
> + *
> + **/
> +void __sg_free_table(struct sg_table *table, sg_free_fn *free_fn)
> +{
> + struct scatterlist *sgl, *next;
> +
> + if (unlikely(!table->sgl))
> + return;
> +
> + sgl = table->sgl;
> + while (table->orig_nents) {
> + unsigned int alloc_size = table->orig_nents;
> + unsigned int sg_size;
> +
> + /*
> + * If we have more than SG_MAX_SINGLE_ALLOC segments left,
> + * then assign 'next' to the sg table after the current one.
> + * sg_size is then one less than alloc size, since the last
> + * element is the chain pointer.
> + */
> + if (alloc_size > SG_MAX_SINGLE_ALLOC) {
> + next = sg_chain_ptr(&sgl[SG_MAX_SINGLE_ALLOC - 1]);
> + alloc_size = SG_MAX_SINGLE_ALLOC;
> + sg_size = alloc_size - 1;
> + } else {
> + sg_size = alloc_size;
> + next = NULL;
> + }
> +
> + table->orig_nents -= sg_size;
> + free_fn(sgl, alloc_size);
> + sgl = next;
> + }
> +
> + table->sgl = NULL;
> +}
> +EXPORT_SYMBOL(__sg_free_table);
> +
> +/**
> + * sg_free_table - Free a previously allocated sg table
> + * @table: The mapped sg table header
> + *
> + **/
> +void sg_free_table(struct sg_table *table)
> +{
> + __sg_free_table(table, sg_kfree);
> +}
> +EXPORT_SYMBOL(sg_free_table);
> +
> +/**
> + * __sg_alloc_table - Allocate and initialize an sg table with given allocator
> + * @table: The sg table header to use
> + * @nents: Number of entries in sg list
> + * @gfp_mask: GFP allocation mask
> + * @alloc_fn: Allocator to use
> + *
> + * Notes:
> + * If this function returns non-0 (eg failure), the caller must call
> + * __sg_free_table() to cleanup any leftover allocations.
> + *
> + **/
> +int __sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask,
> + sg_alloc_fn *alloc_fn)
> +{
> + struct scatterlist *sg, *prv;
> + unsigned int left;
> +
> +#ifndef ARCH_HAS_SG_CHAIN
> + BUG_ON(nents > SG_MAX_SINGLE_ALLOC);
> +#endif
> +
> + memset(table, 0, sizeof(*table));
> +
> + left = nents;
> + prv = NULL;
> + do {
> + unsigned int sg_size, alloc_size = left;
> +
> + if (alloc_size > SG_MAX_SINGLE_ALLOC) {
> + alloc_size = SG_MAX_SINGLE_ALLOC;
> + sg_size = alloc_size - 1;
> + } else
> + sg_size = alloc_size;
> +
> + left -= sg_size;
> +
> + sg = alloc_fn(alloc_size, gfp_mask);
> + if (unlikely(!sg))
> + return -ENOMEM;
> +
> + sg_init_table(sg, alloc_size);
> + table->nents = table->orig_nents += sg_size;
> +
> + /*
> + * If this is the first mapping, assign the sg table header.
> + * If this is not the first mapping, chain previous part.
> + */
> + if (prv)
> + sg_chain(prv, SG_MAX_SINGLE_ALLOC, sg);
> + else
> + table->sgl = sg;
> +
> + /*
> + * If no more entries after this one, mark the end
> + */
> + if (!left)
> + sg_mark_end(&sg[sg_size - 1]);
> +
> + /*
> + * only really needed for mempool backed sg allocations (like
> + * SCSI), a possible improvement here would be to pass the
> + * table pointer into the allocator and let that clear these
> + * flags
> + */
> + gfp_mask &= ~__GFP_WAIT;
> + gfp_mask |= __GFP_HIGH;
> + prv = sg;
> + } while (left);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL(__sg_alloc_table);
> +
> +/**
> + * sg_alloc_table - Allocate and initialize an sg table
> + * @table: The sg table header to use
> + * @nents: Number of entries in sg list
> + * @gfp_mask: GFP allocation mask
> + *
> + * Description:
> + * Allocate and initialize an sg table. If @nents@ is larger than
> + * SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
> + *
> + **/
> +int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
> +{
> + int ret;
> +
> + ret = __sg_alloc_table(table, nents, gfp_mask, sg_kmalloc);
> + if (unlikely(ret))
> + __sg_free_table(table, sg_kfree);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL(sg_alloc_table);

Boaz