From 8e7e9c672fd810a099dc2ac92a80e8e95cd5b0dc Mon Sep 17 00:00:00 2001
From: Qu Wenruo <wqu@suse.com>
Date: Sat, 17 Feb 2024 16:59:49 +1030
Subject: btrfs: subpage: make reader lock utilize bitmap
Currently btrfs_subpage utilizes its atomic member @reader to manage the
reader counter. However it is only utilized to prevent the page to be
released/unlocked when we still have reads underway.
In that use case, we don't really allow multiple readers on the same
subpage sector. So here we can introduce a new locked bitmap to
represent exactly which subpage range is locked for read.
In theory we can remove btrfs_subpage::reader as it's just the set bits
of the new locked bitmap. But unfortunately bitmap doesn't provide such
handy API yet, so we still keep the reader counter.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
fs/btrfs/subpage.c | 45 +++++++++++++++++++++++++++++++++++----------
1 file changed, 35 insertions(+), 10 deletions(-)
(limited to 'fs/btrfs/subpage.c')
diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c
index 24f8be565a61..eae9e8a478f6 100644
--- a/fs/btrfs/subpage.c
+++ b/fs/btrfs/subpage.c
@@ -111,6 +111,9 @@ void btrfs_init_subpage_info(struct btrfs_subpage_info *subpage_info, u32 sector
subpage_info->checked_offset = cur;
cur += nr_bits;
+ subpage_info->locked_offset = cur;
+ cur += nr_bits;
+
subpage_info->total_nr_bits = cur;
}
@@ -237,28 +240,58 @@ static void btrfs_subpage_assert(const struct btrfs_fs_info *fs_info,
start + len <= folio_pos(folio) + PAGE_SIZE);
}
+#define subpage_calc_start_bit(fs_info, folio, name, start, len) \
+({ \
+ unsigned int start_bit; \
+ \
+ btrfs_subpage_assert(fs_info, folio, start, len); \
+ start_bit = offset_in_page(start) >> fs_info->sectorsize_bits; \
+ start_bit += fs_info->subpage_info->name##_offset; \
+ start_bit; \
+})
+
void btrfs_subpage_start_reader(const struct btrfs_fs_info *fs_info,
struct folio *folio, u64 start, u32 len)
{
struct btrfs_subpage *subpage = folio_get_private(folio);
+ const int start_bit = subpage_calc_start_bit(fs_info, folio, locked, start, len);
const int nbits = len >> fs_info->sectorsize_bits;
+ unsigned long flags;
+
btrfs_subpage_assert(fs_info, folio, start, len);
+ spin_lock_irqsave(&subpage->lock, flags);
+ /*
+ * Even though it's just for reading the page, no one should have
+ * locked the subpage range.
+ */
+ ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
+ bitmap_set(subpage->bitmaps, start_bit, nbits);
atomic_add(nbits, &subpage->readers);
+ spin_unlock_irqrestore(&subpage->lock, flags);
}
void btrfs_subpage_end_reader(const struct btrfs_fs_info *fs_info,
struct folio *folio, u64 start, u32 len)
{
struct btrfs_subpage *subpage = folio_get_private(folio);
+ const int start_bit = subpage_calc_start_bit(fs_info, folio, locked, start, len);
const int nbits = len >> fs_info->sectorsize_bits;
+ unsigned long flags;
bool is_data;
bool last;
btrfs_subpage_assert(fs_info, folio, start, len);
is_data = is_data_inode(folio->mapping->host);
+
+ spin_lock_irqsave(&subpage->lock, flags);
+
+ /* The range should have already been locked. */
+ ASSERT(bitmap_test_range_all_set(subpage->bitmaps, start_bit, nbits));
ASSERT(atomic_read(&subpage->readers) >= nbits);
+
+ bitmap_clear(subpage->bitmaps, start_bit, nbits);
last = atomic_sub_and_test(nbits, &subpage->readers);
/*
@@ -270,6 +303,7 @@ void btrfs_subpage_end_reader(const struct btrfs_fs_info *fs_info,
*/
if (is_data && last)
folio_unlock(folio);
+ spin_unlock_irqrestore(&subpage->lock, flags);
}
static void btrfs_subpage_clamp_range(struct folio *folio, u64 *start, u32 *len)
@@ -365,16 +399,6 @@ void btrfs_folio_end_writer_lock(const struct btrfs_fs_info *fs_info,
folio_unlock(folio);
}
-#define subpage_calc_start_bit(fs_info, folio, name, start, len) \
-({ \
- unsigned int start_bit; \
- \
- btrfs_subpage_assert(fs_info, folio, start, len); \
- start_bit = offset_in_page(start) >> fs_info->sectorsize_bits; \
- start_bit += fs_info->subpage_info->name##_offset; \
- start_bit; \
-})
-
#define subpage_test_bitmap_all_set(fs_info, subpage, name) \
bitmap_test_range_all_set(subpage->bitmaps, \
fs_info->subpage_info->name##_offset, \
@@ -751,6 +775,7 @@ void __cold btrfs_subpage_dump_bitmap(const struct btrfs_fs_info *fs_info,
GET_SUBPAGE_BITMAP(subpage, subpage_info, writeback, &writeback_bitmap);
GET_SUBPAGE_BITMAP(subpage, subpage_info, ordered, &ordered_bitmap);
GET_SUBPAGE_BITMAP(subpage, subpage_info, checked, &checked_bitmap);
+ GET_SUBPAGE_BITMAP(subpage, subpage_info, locked, &checked_bitmap);
spin_unlock_irqrestore(&subpage->lock, flags);
dump_page(folio_page(folio, 0), "btrfs subpage dump");
--
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