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Date: Thu, 25 Aug 2011 10:46:52 -0700 (PDT)
From: Dan Magenheimer <dan.magenheimer@...cle.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, jeremy@...p.org,
hughd@...gle.com, ngupta@...are.org,
Konrad Wilk <konrad.wilk@...cle.com>, JBeulich@...ell.com,
Kurt Hackel <kurt.hackel@...cle.com>, npiggin@...nel.dk,
akpm@...ux-foundation.org, riel@...hat.com, hannes@...xchg.org,
matthew@....cx, Chris Mason <chris.mason@...cle.com>,
sjenning@...ux.vnet.ibm.com, jackdachef@...il.com,
cyclonusj@...il.com
Subject: RE: Subject: [PATCH V7 3/4] mm: frontswap: add swap hooks and extend
try_to_unuse
> From: KAMEZAWA Hiroyuki [mailto:kamezawa.hiroyu@...fujitsu.com]
> Subject: Re: Subject: [PATCH V7 3/4] mm: frontswap: add swap hooks and extend try_to_unuse
Thanks again for the great review! I think the only change required
for V8 is the addition of a comment in find_next_to_unuse (see below).
After reading all of my replies, please let me know if you disagree.
Dan
> > From: Dan Magenheimer <dan.magenheimer@...cle.com>
> >
> > This third patch of four in the frontswap series adds hooks in the swap
> > subsystem and extends try_to_unuse so that frontswap_shrink can do a
> > "partial swapoff". Also, declarations for the extern-ified swap variables
> > in the first patch are declared.
> >
> > Note that failed frontswap_map allocation is safe... failure is noted
> > by lack of "FS" in the subsequent printk.
> >
> > [v7: rebase to 3.0-rc3]
> > [v7: JBeulich@...ell.com: use new static inlines, no-ops if not config'd]
> > [v6: rebase to 3.1-rc1]
> > [v6: lliubbo@...il.com: use vzalloc]
> > [v5: accidentally posted stale code for v4 that failed to compile :-(]
> > [v4: rebase to 2.6.39]
> > Signed-off-by: Dan Magenheimer <dan.magenheimer@...cle.com>
> > Reviewed-by: Konrad Wilk <konrad.wilk@...cle.com>
> > Acked-by: Jan Beulich <JBeulich@...ell.com>
> > Acked-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> > Cc: Jeremy Fitzhardinge <jeremy@...p.org>
> > Cc: Hugh Dickins <hughd@...gle.com>
> > Cc: Johannes Weiner <hannes@...xchg.org>
> > Cc: Nitin Gupta <ngupta@...are.org>
> > Cc: Matthew Wilcox <matthew@....cx>
> > Cc: Chris Mason <chris.mason@...cle.com>
> > Cc: Rik Riel <riel@...hat.com>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> >
> > --- linux/mm/swapfile.c 2011-08-08 08:19:26.336684746 -0600
> > +++ frontswap/mm/swapfile.c 2011-08-23 08:21:15.301998803 -0600
> > @@ -32,6 +32,8 @@
> > #include <linux/memcontrol.h>
> > #include <linux/poll.h>
> > #include <linux/oom.h>
> > +#include <linux/frontswap.h>
> > +#include <linux/swapfile.h>
> >
> > #include <asm/pgtable.h>
> > #include <asm/tlbflush.h>
> > @@ -43,7 +45,7 @@ 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;
> > @@ -54,9 +56,9 @@ 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);
> >
> > @@ -557,6 +559,7 @@ 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);
> > @@ -1022,7 +1025,7 @@ 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;
> > @@ -1048,6 +1051,12 @@ static unsigned int find_next_to_unuse(s
> > prev = 0;
> > i = 1;
> > }
>
> > + if (frontswap) {
> > + if (frontswap_test(si, i))
> > + break;
> > + else
> > + continue;
> > + }
>
> Could you add comment ? If frontswap==true, only scan frontswap ?
Yes, thank you, this is a good comment to add.
> > @@ -1059,8 +1068,12 @@ 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; ignored if frontswap is false
> > */
> > -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;
> > @@ -1093,7 +1106,7 @@ 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;
> > @@ -1260,6 +1273,10 @@ static int try_to_unuse(unsigned int typ
> > * interactive performance.
> > */
> > cond_resched();
> > + if (frontswap && pages_to_unuse > 0) {
> > + if (!--pages_to_unuse)
> > + break;
> > + }
> > }
>
> Is this a best-effort function and doesn't need to return condition
> of pages_to_unuse ?
> Caller of try_to_unuse(si, true....) is frontswap_shrink(). Right ?
Right. This function is best-effort with frontswap or without frontswap.
In a non-frontswap system, a swapoff command may fail because try_to_unuse
wasn't able to swap in all pages. The same is true of a "partial swapoff"
when frontswap_shrink() is called. Since this behavior didn't change,
I didn't add a comment for that. A return condition isn't needed because
frontswap_curr_pages can be queried.
Thanks!
Dan
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