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SubjectRe: [RFC] per thread page reservation patch
> diff -puN include/linux/gfp.h~reiser4-perthread-pages include/linux/gfp.h
> --- linux-2.6.10-rc3/include/linux/gfp.h~reiser4-perthread-pages 2004-12-22 20:09:44.153164276 +0300
> +++ linux-2.6.10-rc3-vs/include/linux/gfp.h 2004-12-22 20:09:44.199167794 +0300
> @@ -134,4 +134,8 @@ extern void FASTCALL(free_cold_page(stru
>
> void page_alloc_init(void);
>
> +int perthread_pages_reserve(int nrpages, int gfp);
> +void perthread_pages_release(int nrpages);
> +int perthread_pages_count(void);
> +
> #endif /* __LINUX_GFP_H */
> diff -puN include/linux/init_task.h~reiser4-perthread-pages include/linux/init_task.h
> --- linux-2.6.10-rc3/include/linux/init_task.h~reiser4-perthread-pages 2004-12-22 20:09:44.160164812 +0300
> +++ linux-2.6.10-rc3-vs/include/linux/init_task.h 2004-12-22 20:09:44.201167947 +0300
> @@ -112,8 +112,8 @@ extern struct group_info init_groups;
> .proc_lock = SPIN_LOCK_UNLOCKED, \
> .switch_lock = SPIN_LOCK_UNLOCKED, \
> .journal_info = NULL, \
> + .private_pages = LIST_HEAD_INIT(tsk.private_pages), \
> + .private_pages_count = 0, \
> }
>
> -
> -
> #endif
> diff -puN include/linux/sched.h~reiser4-perthread-pages include/linux/sched.h
> --- linux-2.6.10-rc3/include/linux/sched.h~reiser4-perthread-pages 2004-12-22 20:09:44.170165576 +0300
> +++ linux-2.6.10-rc3-vs/include/linux/sched.h 2004-12-22 20:09:44.204168176 +0300
> @@ -691,6 +691,9 @@ struct task_struct {
> nodemask_t mems_allowed;
> int cpuset_mems_generation;
> #endif
> +
> + struct list_head private_pages; /* per-process private pages */
> + int private_pages_count;
> };
>
> static inline pid_t process_group(struct task_struct *tsk)
> diff -puN kernel/fork.c~reiser4-perthread-pages kernel/fork.c
> --- linux-2.6.10-rc3/kernel/fork.c~reiser4-perthread-pages 2004-12-22 20:09:44.179166264 +0300
> +++ linux-2.6.10-rc3-vs/kernel/fork.c 2004-12-22 20:09:44.215169017 +0300
> @@ -154,6 +154,10 @@ static struct task_struct *dup_task_stru
> tsk->thread_info = ti;
> ti->task = tsk;
>
> + /* initialize list of pages privately reserved by process */
> + INIT_LIST_HEAD(&tsk->private_pages);
> + tsk->private_pages_count = 0;
> +
> /* One for us, one for whoever does the "release_task()" (usually parent) */
> atomic_set(&tsk->usage,2);
> return tsk;
> diff -puN mm/page_alloc.c~reiser4-perthread-pages mm/page_alloc.c
> --- linux-2.6.10-rc3/mm/page_alloc.c~reiser4-perthread-pages 2004-12-22 20:09:44.187166876 +0300
> +++ linux-2.6.10-rc3-vs/mm/page_alloc.c 2004-12-22 20:09:44.219169323 +0300
> @@ -551,6 +551,97 @@ void fastcall free_cold_page(struct page
> free_hot_cold_page(page, 1);
> }
>
> +static inline struct list_head *get_per_thread_pages(void)
> +{
> + return &current->private_pages;
> +}

this is a completely useless wrapper that doesn't buy anything.

> +int perthread_pages_reserve(int nrpages, int gfp)
> +{
> + int i;
> + struct list_head accumulator;
> + struct list_head *per_thread;
> +
> + per_thread = get_per_thread_pages();
> + INIT_LIST_HEAD(&accumulator);
> + list_splice_init(per_thread, &accumulator);

Can probably be written much simpler as:

int perthread_pages_reserve(int nrpages, int gfp)
{
LIST_HEAD(accumulator);
int i;
list_splice_init(&current->private_pages, &accumulator);

Now the big question is, what's synchronizing access to
current->private_pages?

> + for (i = 0; i < nrpages; ++i) {
> + struct page *page;
> +
> + page = alloc_page(gfp);
> + if (page != NULL)
> + list_add(&page->lru, &accumulator);
> + else {
> + for (; i > 0; --i) {
> + page = list_entry(accumulator.next, struct page, lru);
> + list_del(&page->lru);
> + page_cache_release(page);
> + }
> + return -ENOMEM;
> + }
> + }

Would be much more readable with the error condition handling at the
end of the function and a goto.

> +int perthread_pages_count(void)
> +{
> + return current->private_pages_count;
> +}
> +EXPORT_SYMBOL(perthread_pages_count);

Again a completely useless wrapper.

> +static inline struct page *
> +perthread_pages_alloc(void)
> +{
> + struct list_head *perthread_pages;
> +
> + /*
> + * try to allocate pages from the per-thread private_pages pool. No
> + * locking is needed: this list can only be modified by the thread
> + * itself, and not by interrupts or other threads.
> + */
> + perthread_pages = get_per_thread_pages();
> + if (!in_interrupt() && !list_empty(perthread_pages)) {
> + struct page *page;
> +
> + page = list_entry(perthread_pages->next, struct page, lru);
> + list_del(&page->lru);
> + current->private_pages_count--;
> + /*
> + * per-thread page is already initialized, just return it.
> + */
> + return page;
> + } else
> + return NULL;
> +}

Would be written much cleaner with a single return statement and the
comment above the function, ala:

/*
* try to allocate pages from the per-thread private_pages pool. No
* locking is needed: this list can only be modified by the thread
* itself, and not by interrupts or other threads.
*/
static inline struct page *perthread_pages_alloc(void)
{
struct list_head *perthread_pages = &current->private_pages;
struct page *page = NULL;
if (!in_interrupt() && !list_empty(perthread_pages)) {
page = list_entry(perthread_pages->next, struct page, lru);
list_del(&page->lru);
current->private_pages_count--;
}
return page;
}
> + if (order == 0) {
> + page = perthread_pages_alloc();
> + if (page != NULL)
> + return page;
> + }
> +

You should at least move the !in_interrupt() condition out here.

-
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