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Date: Tue, 7 Jun 2011 13:59:56 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Dan Magenheimer <dan.magenheimer@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, jeremy@...p.org,
hughd@...gle.com, ngupta@...are.org, JBeulich@...ell.com,
kurt.hackel@...cle.com, npiggin@...e.de, akpm@...ux-foundation.org,
riel@...hat.com, hannes@...xchg.org, matthew@....cx,
chris.mason@...cle.com
Subject: Re: [PATCH V4 3/4] mm: frontswap: add hooks in swap subsystem and
extend
On Fri, May 27, 2011 at 12:49:05PM -0700, Dan Magenheimer wrote:
> [PATCH V4 3/4] mm: frontswap: add hooks in swap subsystem and extend
> try_to_unuse so that frontswap_shrink can do a "partial swapoff"
>
> Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
>
> Diffstat:
> page_io.c | 12 ++++
> swapfile.c | 58 +++++++++++++++++----
> 2 files changed, 61 insertions(+), 9 deletions(-)
>
> --- linux-2.6.39/mm/swapfile.c 2011-05-18 22:06:34.000000000 -0600
> +++ linux-2.6.39-frontswap/mm/swapfile.c 2011-05-26 15:48:09.665832190 -0600
> @@ -31,6 +31,8 @@
> #include <linux/syscalls.h>
> #include <linux/memcontrol.h>
> #include <linux/poll.h>
> +#include <linux/frontswap.h>
> +#include <linux/swapfile.h>
>
> #include <asm/pgtable.h>
> #include <asm/tlbflush.h>
> @@ -42,7 +44,7 @@ static bool swap_count_continued(struct
> static void free_swap_count_continuations(struct swap_info_struct *);
> static sector_t map_swap_entry(swp_entry_t, struct block_device**);
>
> -static DEFINE_SPINLOCK(swap_lock);
> +DEFINE_SPINLOCK(swap_lock);
> static unsigned int nr_swapfiles;
> long nr_swap_pages;
> long total_swap_pages;
> @@ -53,9 +55,9 @@ static const char Unused_file[] = "Unuse
> static const char Bad_offset[] = "Bad swap offset entry ";
> static const char Unused_offset[] = "Unused swap offset entry ";
>
> -static struct swap_list_t swap_list = {-1, -1};
> +struct swap_list_t swap_list = {-1, -1};
>
> -static struct swap_info_struct *swap_info[MAX_SWAPFILES];
> +struct swap_info_struct *swap_info[MAX_SWAPFILES];
>
> static DEFINE_MUTEX(swapon_mutex);
>
> @@ -556,6 +558,7 @@ static unsigned char swap_entry_free(str
> swap_list.next = p->type;
> nr_swap_pages++;
> p->inuse_pages--;
> + frontswap_flush_page(p->type, offset);
> if ((p->flags & SWP_BLKDEV) &&
> disk->fops->swap_slot_free_notify)
> disk->fops->swap_slot_free_notify(p->bdev, offset);
> @@ -1021,7 +1024,7 @@ static int unuse_mm(struct mm_struct *mm
> * Recycle to start on reaching the end, returning 0 when empty.
> */
> static unsigned int find_next_to_unuse(struct swap_info_struct *si,
> - unsigned int prev)
> + unsigned int prev, bool frontswap)
> {
> unsigned int max = si->max;
> unsigned int i = prev;
> @@ -1047,6 +1050,12 @@ static unsigned int find_next_to_unuse(s
> prev = 0;
> i = 1;
> }
> + if (frontswap) {
> + if (frontswap_test(si, i))
> + break;
> + else
> + continue;
> + }
> count = si->swap_map[i];
> if (count && swap_count(count) != SWAP_MAP_BAD)
> break;
> @@ -1058,8 +1067,12 @@ static unsigned int find_next_to_unuse(s
> * We completely avoid races by reading each swap page in advance,
> * and then search for the process using it. All the necessary
> * page table adjustments can then be made atomically.
> + *
> + * if the boolean frontswap is true, only unuse pages_to_unuse pages;
> + * pages_to_unuse==0 means all pages
> */
> -static int try_to_unuse(unsigned int type)
> +int try_to_unuse(unsigned int type, bool frontswap,
> + unsigned long pages_to_unuse)
> {
> struct swap_info_struct *si = swap_info[type];
> struct mm_struct *start_mm;
> @@ -1092,7 +1105,7 @@ static int try_to_unuse(unsigned int typ
> * one pass through swap_map is enough, but not necessarily:
> * there are races when an instance of an entry might be missed.
> */
> - while ((i = find_next_to_unuse(si, i)) != 0) {
> + while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
> if (signal_pending(current)) {
> retval = -EINTR;
> break;
> @@ -1259,6 +1272,10 @@ static int try_to_unuse(unsigned int typ
> * interactive performance.
> */
> cond_resched();
> + if (frontswap && pages_to_unuse > 0) {
> + if (!--pages_to_unuse)
> + break;
> + }
> }
>
> mmput(start_mm);
> @@ -1528,6 +1545,7 @@ static void enable_swap_info(struct swap
> else
> p->prio = --least_priority;
> p->swap_map = swap_map;
> + p->frontswap_map = frontswap_map;
> p->flags |= SWP_WRITEOK;
> nr_swap_pages += p->pages;
> total_swap_pages += p->pages;
> @@ -1544,6 +1562,7 @@ static void enable_swap_info(struct swap
> swap_list.head = swap_list.next = p->type;
> else
> swap_info[prev]->next = p->type;
> + frontswap_init(p->type);
> spin_unlock(&swap_lock);
> }
>
> @@ -1614,7 +1633,7 @@ SYSCALL_DEFINE1(swapoff, const char __us
> spin_unlock(&swap_lock);
>
> current->flags |= PF_OOM_ORIGIN;
> - err = try_to_unuse(type);
> + err = try_to_unuse(type, false, 0);
You should add a comment right after 0 saying "/* everything */" or
something like that.
> current->flags &= ~PF_OOM_ORIGIN;
>
> if (err) {
> @@ -1651,9 +1670,12 @@ SYSCALL_DEFINE1(swapoff, const char __us
> swap_map = p->swap_map;
> p->swap_map = NULL;
> p->flags = 0;
> + frontswap_flush_area(type);
> spin_unlock(&swap_lock);
> mutex_unlock(&swapon_mutex);
> vfree(swap_map);
> + if (p->frontswap_map)
> + vfree(p->frontswap_map);
> /* Destroy swap account informatin */
> swap_cgroup_swapoff(type);
>
> @@ -2026,6 +2048,7 @@ SYSCALL_DEFINE2(swapon, const char __use
> sector_t span;
> unsigned long maxpages;
> unsigned char *swap_map = NULL;
> + unsigned long *frontswap_map = NULL;
> struct page *page = NULL;
> struct inode *inode = NULL;
>
> @@ -2106,6 +2129,12 @@ SYSCALL_DEFINE2(swapon, const char __use
> error = nr_extents;
> goto bad_swap;
> }
> + /* frontswap enabled? set up bit-per-page map for frontswap */
> + if (frontswap_enabled) {
> + frontswap_map = vmalloc(maxpages / sizeof(long));
Shouldn't we use p->max instead? You are using that value in
__frontswap_flush_area and while it seems that maxpages == p->max
from uniformity standpoint it looks better.
> + if (frontswap_map)
> + memset(frontswap_map, 0, maxpages / sizeof(long));
If we failed to allocate the frontswap_map should we turn frontswap_enabled off?
> + }
>
> if (p->bdev) {
> if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
> @@ -2124,11 +2153,12 @@ SYSCALL_DEFINE2(swapon, const char __use
> enable_swap_info(p, prio, swap_map);
>
> printk(KERN_INFO "Adding %uk swap on %s. "
> - "Priority:%d extents:%d across:%lluk %s%s\n",
> + "Priority:%d extents:%d across:%lluk %s%s%s\n",
> p->pages<<(PAGE_SHIFT-10), name, p->prio,
> nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
> (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
> - (p->flags & SWP_DISCARDABLE) ? "D" : "");
> + (p->flags & SWP_DISCARDABLE) ? "D" : "",
> + (p->frontswap_map) ? "FS" : "");
>
> mutex_unlock(&swapon_mutex);
> atomic_inc(&proc_poll_event);
> @@ -2319,6 +2349,10 @@ int valid_swaphandles(swp_entry_t entry,
> base++;
>
> spin_lock(&swap_lock);
> + if (frontswap_test(si, target)) {
> + spin_unlock(&swap_lock);
> + return 0;
> + }
> if (end > si->max) /* don't go beyond end of map */
> end = si->max;
>
> @@ -2329,6 +2363,9 @@ int valid_swaphandles(swp_entry_t entry,
> break;
> if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
> break;
> + /* Don't read in frontswap pages */
> + if (frontswap_test(si, toff))
> + break;
> }
> /* Count contiguous allocated slots below our target */
> for (toff = target; --toff >= base; nr_pages++) {
> @@ -2337,6 +2374,9 @@ int valid_swaphandles(swp_entry_t entry,
> break;
> if (swap_count(si->swap_map[toff]) == SWAP_MAP_BAD)
> break;
> + /* Don't read in frontswap pages */
> + if (frontswap_test(si, toff))
> + break;
> }
> spin_unlock(&swap_lock);
>
> --- linux-2.6.39/mm/page_io.c 2011-05-18 22:06:34.000000000 -0600
> +++ linux-2.6.39-frontswap/mm/page_io.c 2011-05-26 15:37:25.272870914 -0600
> @@ -18,6 +18,7 @@
> #include <linux/bio.h>
> #include <linux/swapops.h>
> #include <linux/writeback.h>
> +#include <linux/frontswap.h>
> #include <asm/pgtable.h>
>
> static struct bio *get_swap_bio(gfp_t gfp_flags,
> @@ -98,6 +99,12 @@ int swap_writepage(struct page *page, st
> unlock_page(page);
> goto out;
> }
> + if (frontswap_put_page(page) == 0) {
> + set_page_writeback(page);
> + unlock_page(page);
> + end_page_writeback(page);
> + goto out;
> + }
> bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
> if (bio == NULL) {
> set_page_dirty(page);
> @@ -122,6 +129,11 @@ int swap_readpage(struct page *page)
>
> VM_BUG_ON(!PageLocked(page));
> VM_BUG_ON(PageUptodate(page));
> + if (frontswap_get_page(page) == 0) {
> + SetPageUptodate(page);
> + unlock_page(page);
> + goto out;
> + }
> bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
> if (bio == NULL) {
> unlock_page(page);
--
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