[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <e50abade-c44e-41d4-b7bf-b9d54920e2a4@redhat.com>
Date: Wed, 7 Aug 2024 11:28:59 +0200
From: David Hildenbrand <david@...hat.com>
To: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
linux-mm@...ck.org
Cc: justinjiang@...o.com, chrisl@...nel.org, hughd@...gle.com,
kaleshsingh@...gle.com, kasong@...cent.com, linux-kernel@...r.kernel.org,
ryan.roberts@....com, v-songbaohua@...o.com, ying.huang@...el.com
Subject: Re: [PATCH v2 2/2] mm: attempt to batch free swap entries for
zap_pte_range()
> mm/swapfile.c | 78 +++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 67 insertions(+), 11 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 35cb58373493..25c3f98fa8d5 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -156,6 +156,25 @@ static bool swap_is_has_cache(struct swap_info_struct *si,
> return true;
> }
>
> +static bool swap_is_last_map(struct swap_info_struct *si,
> + unsigned long offset, int nr_pages,
> + bool *has_cache)
Please use double tabs for indenting parameters on 2nd line on
new/changed code:
unsigned long offset, int nr_pages, bool *has_cache)
Results in less churn when renaming functions and we can frequently
avoid some lines.
> +{
> + unsigned char *map = si->swap_map + offset;
> + unsigned char *map_end = map + nr_pages;
> + bool cached = false;
> +
> + do {
> + if ((*map & ~SWAP_HAS_CACHE) != 1)
> + return false;
> + if (*map & SWAP_HAS_CACHE)
> + cached = true;
> + } while (++map < map_end);
> +
> + *has_cache = cached;
> + return true;
> +}
> +
> /*
> * returns number of pages in the folio that backs the swap entry. If positive,
> * the folio was reclaimed. If negative, the folio was not reclaimed. If 0, no
> @@ -1469,6 +1488,53 @@ static unsigned char __swap_entry_free(struct swap_info_struct *si,
> return usage;
> }
>
> +static bool __swap_entries_free(struct swap_info_struct *si,
> + swp_entry_t entry, int nr)
Dito.
> +{
> + unsigned long offset = swp_offset(entry);
> + unsigned int type = swp_type(entry);
> + struct swap_cluster_info *ci;
> + bool has_cache = false;
> + unsigned char count;
> + bool can_batch;
> + int i;
> +
> + if (nr <= 1 || swap_count(data_race(si->swap_map[offset])) != 1)
> + goto fallback;
> + /* cross into another cluster */
> + if (nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER)
> + goto fallback;
> +
> + ci = lock_cluster_or_swap_info(si, offset);
> + can_batch = swap_is_last_map(si, offset, nr, &has_cache);
> + if (can_batch) {
> + for (i = 0; i < nr; i++)
> + WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
> + }
> + unlock_cluster_or_swap_info(si, ci);
> +
> + if (!can_batch)
> + goto fallback;
I'd avoid "can_batch" and just do:
ci = lock_cluster_or_swap_info(si, offset);
if (!swap_is_last_map(si, offset, nr, &has_cache)) {
unlock_cluster_or_swap_info(si, ci);
goto fallback;
}
for (i = 0; i < nr; i++)
WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
unlock_cluster_or_swap_info(si, ci);
> + if (!has_cache) {
> + spin_lock(&si->lock);
I'm no expert on that code, but we might drop the cluster lock the take
the swap_info lock and then retake the cluster lock. I assume there are
no races we are worrying about here, right?
> + swap_entry_range_free(si, entry, nr);
> + spin_unlock(&si->lock);
> + }
> + return has_cache;
> +
> +fallback:
> + for (i = 0; i < nr; i++) {
One space too much before the "<".
> + if (data_race(si->swap_map[offset + i])) {
> + count = __swap_entry_free(si, swp_entry(type, offset + i));
> + if (count == SWAP_HAS_CACHE)
> + has_cache = true;
> + } else {
> + WARN_ON_ONCE(1);
> + }
> + }
> + return has_cache;
> +}
> +
--
Cheers,
David / dhildenb
Powered by blists - more mailing lists