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Date: Tue, 23 Sep 2014 22:53:05 -0400
From: Dan Streetman <ddstreet@...e.org>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>, Hugh Dickins <hughd@...gle.com>,
Shaohua Li <shli@...nel.org>,
Jerome Marchand <jmarchan@...hat.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Nitin Gupta <ngupta@...are.org>,
Luigi Semenzato <semenzato@...gle.com>, juno.choi@....com
Subject: Re: [PATCH v1 2/5] mm: add full variable in swap_info_struct
On Sun, Sep 21, 2014 at 8:03 PM, Minchan Kim <minchan@...nel.org> wrote:
> Now, swap leans on !p->highest_bit to indicate a swap is full.
> It works well for normal swap because every slot on swap device
> is used up when the swap is full but in case of zram, swap sees
> still many empty slot although backed device(ie, zram) is full
> since zram's limit is over so that it could make trouble when
> swap use highest_bit to select new slot via free_cluster.
>
> This patch introduces full varaiable in swap_info_struct
> to solve the problem.
>
> Suggested-by: Dan Streetman <ddstreet@...e.org>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> include/linux/swap.h | 1 +
> mm/swapfile.c | 33 +++++++++++++++++++--------------
> 2 files changed, 20 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index ea4f926e6b9b..a3c11c051495 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -224,6 +224,7 @@ struct swap_info_struct {
> struct swap_cluster_info free_cluster_tail; /* free cluster list tail */
> unsigned int lowest_bit; /* index of first free in swap_map */
> unsigned int highest_bit; /* index of last free in swap_map */
> + bool full; /* whether swap is full or not */
> unsigned int pages; /* total of usable pages of swap */
> unsigned int inuse_pages; /* number of those currently in use */
> unsigned int cluster_next; /* likely index for next allocation */
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index c07f7f4912e9..209112cf8b83 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -558,7 +558,7 @@ checks:
> }
> if (!(si->flags & SWP_WRITEOK))
> goto no_page;
> - if (!si->highest_bit)
> + if (si->full)
> goto no_page;
> if (offset > si->highest_bit)
> scan_base = offset = si->lowest_bit;
> @@ -589,6 +589,7 @@ checks:
> spin_lock(&swap_avail_lock);
> plist_del(&si->avail_list, &swap_avail_head);
> spin_unlock(&swap_avail_lock);
> + si->full = true;
> }
> si->swap_map[offset] = usage;
> inc_cluster_info_page(si, si->cluster_info, offset);
> @@ -653,14 +654,14 @@ start_over:
> plist_requeue(&si->avail_list, &swap_avail_head);
> spin_unlock(&swap_avail_lock);
> spin_lock(&si->lock);
> - if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
> + if (si->full || !(si->flags & SWP_WRITEOK)) {
> spin_lock(&swap_avail_lock);
> if (plist_node_empty(&si->avail_list)) {
> spin_unlock(&si->lock);
> goto nextsi;
> }
> - WARN(!si->highest_bit,
> - "swap_info %d in list but !highest_bit\n",
> + WARN(si->full,
> + "swap_info %d in list but swap is full\n",
> si->type);
> WARN(!(si->flags & SWP_WRITEOK),
> "swap_info %d in list but !SWP_WRITEOK\n",
> @@ -796,21 +797,25 @@ static unsigned char swap_entry_free(struct swap_info_struct *p,
>
> /* free if no reference */
> if (!usage) {
> + bool was_full;
> +
> dec_cluster_info_page(p, p->cluster_info, offset);
> if (offset < p->lowest_bit)
> p->lowest_bit = offset;
> - if (offset > p->highest_bit) {
> - bool was_full = !p->highest_bit;
> + if (offset > p->highest_bit)
> p->highest_bit = offset;
> - if (was_full && (p->flags & SWP_WRITEOK)) {
> - spin_lock(&swap_avail_lock);
> - WARN_ON(!plist_node_empty(&p->avail_list));
> - if (plist_node_empty(&p->avail_list))
> - plist_add(&p->avail_list,
> - &swap_avail_head);
> - spin_unlock(&swap_avail_lock);
> - }
> + was_full = p->full;
> +
> + if (was_full && (p->flags & SWP_WRITEOK)) {
was_full was only needed because highest_bit was reset to offset right
before checking for fullness, so now that ->full is used instead of
!highest_bit, was_full isn't needed anymore, you can just check
p->full.
> + spin_lock(&swap_avail_lock);
> + WARN_ON(!plist_node_empty(&p->avail_list));
> + if (plist_node_empty(&p->avail_list))
> + plist_add(&p->avail_list,
> + &swap_avail_head);
> + spin_unlock(&swap_avail_lock);
> + p->full = false;
> }
> +
> atomic_long_inc(&nr_swap_pages);
> p->inuse_pages--;
> frontswap_invalidate_page(p->type, offset);
> --
> 2.0.0
>
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