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Date: Thu, 1 Nov 2012 14:03:47 +0900
From: Minchan Kim <minchan@...nel.org>
To: Joonsoo Kim <js1304@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Mel Gorman <mel@....ul.ie>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH v2 4/5] mm, highmem: makes flush_all_zero_pkmaps() return
index of first flushed entry
On Thu, Nov 01, 2012 at 01:56:36AM +0900, Joonsoo Kim wrote:
> In current code, after flush_all_zero_pkmaps() is invoked,
> then re-iterate all pkmaps. It can be optimized if flush_all_zero_pkmaps()
> return index of first flushed entry. With this index,
> we can immediately map highmem page to virtual address represented by index.
> So change return type of flush_all_zero_pkmaps()
> and return index of first flushed entry.
>
> Additionally, update last_pkmap_nr to this index.
> It is certain that entry which is below this index is occupied by other mapping,
> therefore updating last_pkmap_nr to this index is reasonable optimization.
>
> Cc: Mel Gorman <mel@....ul.ie>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Minchan Kim <minchan@...nel.org>
> Signed-off-by: Joonsoo Kim <js1304@...il.com>
>
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index ef788b5..97ad208 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -32,6 +32,7 @@ static inline void invalidate_kernel_vmap_range(void *vaddr, int size)
>
> #ifdef CONFIG_HIGHMEM
> #include <asm/highmem.h>
> +#define PKMAP_INVALID_INDEX (LAST_PKMAP)
>
> /* declarations for linux/mm/highmem.c */
> unsigned int nr_free_highpages(void);
> diff --git a/mm/highmem.c b/mm/highmem.c
> index d98b0a9..b365f7b 100644
> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -106,10 +106,10 @@ struct page *kmap_to_page(void *vaddr)
> return virt_to_page(addr);
> }
>
> -static void flush_all_zero_pkmaps(void)
> +static unsigned int flush_all_zero_pkmaps(void)
> {
> int i;
> - int need_flush = 0;
> + unsigned int index = PKMAP_INVALID_INDEX;
>
> flush_cache_kmaps();
>
> @@ -141,10 +141,13 @@ static void flush_all_zero_pkmaps(void)
> &pkmap_page_table[i]);
>
> set_page_address(page, NULL);
> - need_flush = 1;
> + if (index == PKMAP_INVALID_INDEX)
> + index = i;
> }
> - if (need_flush)
> + if (index != PKMAP_INVALID_INDEX)
> flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
> +
> + return index;
> }
>
> /**
> @@ -152,14 +155,19 @@ static void flush_all_zero_pkmaps(void)
> */
> void kmap_flush_unused(void)
> {
> + unsigned int index;
> +
> lock_kmap();
> - flush_all_zero_pkmaps();
> + index = flush_all_zero_pkmaps();
> + if (index != PKMAP_INVALID_INDEX && (index < last_pkmap_nr))
> + last_pkmap_nr = index;
I don't know how kmap_flush_unused is really fast path so how my nitpick
is effective. Anyway,
What problem happens if we do following as?
lock()
index = flush_all_zero_pkmaps();
if (index != PKMAP_INVALID_INDEX)
last_pkmap_nr = index;
unlock();
Normally, last_pkmap_nr is increased with searching empty slot in
map_new_virtual. So I expect return value of flush_all_zero_pkmaps
in kmap_flush_unused normally become either less than last_pkmap_nr
or last_pkmap_nr + 1.
> unlock_kmap();
> }
>
> static inline unsigned long map_new_virtual(struct page *page)
> {
> unsigned long vaddr;
> + unsigned int index = PKMAP_INVALID_INDEX;
> int count;
>
> start:
> @@ -168,40 +176,45 @@ start:
> for (;;) {
> last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
> if (!last_pkmap_nr) {
> - flush_all_zero_pkmaps();
> - count = LAST_PKMAP;
> + index = flush_all_zero_pkmaps();
> + break;
> }
> - if (!pkmap_count[last_pkmap_nr])
> + if (!pkmap_count[last_pkmap_nr]) {
> + index = last_pkmap_nr;
> break; /* Found a usable entry */
> - if (--count)
> - continue;
> -
> - /*
> - * Sleep for somebody else to unmap their entries
> - */
> - {
> - DECLARE_WAITQUEUE(wait, current);
> -
> - __set_current_state(TASK_UNINTERRUPTIBLE);
> - add_wait_queue(&pkmap_map_wait, &wait);
> - unlock_kmap();
> - schedule();
> - remove_wait_queue(&pkmap_map_wait, &wait);
> - lock_kmap();
> -
> - /* Somebody else might have mapped it while we slept */
> - if (page_address(page))
> - return (unsigned long)page_address(page);
> -
> - /* Re-start */
> - goto start;
> }
> + if (--count == 0)
> + break;
> }
> - vaddr = PKMAP_ADDR(last_pkmap_nr);
> +
> + /*
> + * Sleep for somebody else to unmap their entries
> + */
> + if (index == PKMAP_INVALID_INDEX) {
> + DECLARE_WAITQUEUE(wait, current);
> +
> + __set_current_state(TASK_UNINTERRUPTIBLE);
> + add_wait_queue(&pkmap_map_wait, &wait);
> + unlock_kmap();
> + schedule();
> + remove_wait_queue(&pkmap_map_wait, &wait);
> + lock_kmap();
> +
> + /* Somebody else might have mapped it while we slept */
> + vaddr = (unsigned long)page_address(page);
> + if (vaddr)
> + return vaddr;
> +
> + /* Re-start */
> + goto start;
> + }
> +
> + vaddr = PKMAP_ADDR(index);
> set_pte_at(&init_mm, vaddr,
> - &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
> + &(pkmap_page_table[index]), mk_pte(page, kmap_prot));
>
> - pkmap_count[last_pkmap_nr] = 1;
> + pkmap_count[index] = 1;
> + last_pkmap_nr = index;
> set_page_address(page, (void *)vaddr);
>
> return vaddr;
> --
> 1.7.9.5
>
> --
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--
Kind regards,
Minchan Kim
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