From: Michal Hocko <mhocko@kernel.org>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
dave.hansen@intel.com, ak@linux.intel.com, aaron.lu@intel.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Hugh Dickins <hughd@google.com>, Shaohua Li <shli@kernel.org>,
Minchan Kim <minchan@kernel.org>, Rik van Riel <riel@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Hillf Danton <hillf.zj@alibaba-inc.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Jonathan Corbet <corbet@lwn.net>,
Tim C Chen <tim.c.chen@intel.com>
Subject: Re: [Update][PATCH v5 7/9] mm/swap: Add cache for swap slots allocation
Date: Tue, 17 Jan 2017 11:16:32 +0100 [thread overview]
Message-ID: <20170117101631.GG19699@dhcp22.suse.cz> (raw)
In-Reply-To: <87tw8ymm2z.fsf_-_@yhuang-dev.intel.com>
On Tue 17-01-17 10:55:47, Huang, Ying wrote:
[...]
> +int free_swap_slot(swp_entry_t entry)
> +{
> + struct swap_slots_cache *cache;
> +
> + BUG_ON(!swap_slot_cache_initialized);
> +
> + cache = &get_cpu_var(swp_slots);
> + if (use_swap_slot_cache && cache->slots_ret) {
> + spin_lock_irq(&cache->free_lock);
> + /* Swap slots cache may be deactivated before acquiring lock */
> + if (!use_swap_slot_cache) {
> + spin_unlock_irq(&cache->free_lock);
> + goto direct_free;
> + }
> + if (cache->n_ret >= SWAP_SLOTS_CACHE_SIZE) {
> + /*
> + * Return slots to global pool.
> + * The current swap_map value is SWAP_HAS_CACHE.
> + * Set it to 0 to indicate it is available for
> + * allocation in global pool
> + */
> + swapcache_free_entries(cache->slots_ret, cache->n_ret);
> + cache->n_ret = 0;
> + }
> + cache->slots_ret[cache->n_ret++] = entry;
> + spin_unlock_irq(&cache->free_lock);
> + } else {
> +direct_free:
> + swapcache_free_entries(&entry, 1);
> + }
> + put_cpu_var(swp_slots);
> +
> + return 0;
> +}
> +
> +swp_entry_t get_swap_page(void)
> +{
> + swp_entry_t entry, *pentry;
> + struct swap_slots_cache *cache;
> +
> + /*
> + * Preemption need to be turned on here, because we may sleep
> + * in refill_swap_slots_cache(). But it is safe, because
> + * accesses to the per-CPU data structure are protected by a
> + * mutex.
> + */
the comment doesn't really explain why it is safe. THere are other users
which are not using the lock. E.g. just look at free_swap_slot above.
How can
cache->slots_ret[cache->n_ret++] = entry;
be safe wrt.
pentry = &cache->slots[cache->cur++];
entry = *pentry;
Both of them might touch the same slot, no? Btw. I would rather prefer
this would be a follow up fix with the trace and the detailed
explanation.
> + cache = raw_cpu_ptr(&swp_slots);
> +
> + entry.val = 0;
> + if (check_cache_active()) {
> + mutex_lock(&cache->alloc_lock);
> + if (cache->slots) {
> +repeat:
> + if (cache->nr) {
> + pentry = &cache->slots[cache->cur++];
> + entry = *pentry;
> + pentry->val = 0;
> + cache->nr--;
> + } else {
> + if (refill_swap_slots_cache(cache))
> + goto repeat;
> + }
> + }
> + mutex_unlock(&cache->alloc_lock);
> + if (entry.val)
> + return entry;
> + }
> +
> + get_swap_pages(1, &entry);
> +
> + return entry;
> +}
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-01-17 10:16 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-11 17:55 [PATCH v5 0/9] mm/swap: Regular page swap optimizations Tim Chen
2017-01-11 17:55 ` [PATCH v5 1/9] mm/swap: Fix kernel message in swap_info_get() Tim Chen
2017-01-11 17:55 ` [PATCH v5 2/9] mm/swap: Add cluster lock Tim Chen
2017-01-11 23:00 ` Andrew Morton
2017-01-11 23:07 ` Jonathan Corbet
2017-01-11 23:15 ` Andrew Morton
2017-01-12 1:47 ` Huang, Ying
2017-01-12 1:58 ` Andrew Morton
2017-01-12 2:51 ` Huang, Ying
2017-01-14 4:37 ` [Update][PATCH " Huang, Ying
2017-01-12 1:23 ` [PATCH " Huang, Ying
2017-01-11 17:55 ` [PATCH v5 3/9] mm/swap: Split swap cache into 64MB trunks Tim Chen
2017-01-11 23:09 ` Andrew Morton
2017-01-11 23:19 ` Andi Kleen
2017-01-12 16:47 ` Tim Chen
2017-01-11 17:55 ` [PATCH v5 4/9] mm/swap: skip read ahead for unreferenced swap slots Tim Chen
2017-01-11 17:55 ` [PATCH v5 5/9] mm/swap: Allocate swap slots in batches Tim Chen
2017-01-11 17:55 ` [PATCH v5 6/9] mm/swap: Free swap slots in batch Tim Chen
2017-01-11 17:55 ` [PATCH v5 7/9] mm/swap: Add cache for swap slots allocation Tim Chen
2017-01-17 2:55 ` [Update][PATCH " Huang, Ying
2017-01-17 10:16 ` Michal Hocko [this message]
2017-01-17 17:24 ` Chen, Tim C
2017-01-17 20:03 ` Michal Hocko
2017-01-17 20:31 ` Chen, Tim C
2017-01-17 21:42 ` Tim Chen
2017-01-18 12:45 ` Michal Hocko
2017-01-18 18:03 ` Tim Chen
2017-01-18 18:15 ` Michal Hocko
2017-01-11 17:55 ` [PATCH v5 8/9] mm/swap: Enable swap slots cache usage Tim Chen
2017-01-11 17:55 ` [PATCH v5 9/9] mm/swap: Skip readahead only when swap slot cache is enabled Tim Chen
2017-01-16 12:02 ` [PATCH v5 0/9] mm/swap: Regular page swap optimizations Michal Hocko
2017-01-17 1:06 ` Huang, Ying
2017-01-17 7:49 ` Michal Hocko
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