Hi Kent,
On Fri, 10 Nov 2023, Kent Overstreet wrote:
Previosuly, the transaction commit path would have to add keys to the
btree write buffer as a separate operation, requiring additional global
synchronization.
This patch introduces a new journal entry type, which indicates that the
keys need to be copied into the btree write buffer prior to being
written out. We switch the journal entry type back to
JSET_ENTRY_btree_keys prior to write, so this is not an on disk format
change.
Flushing the btree write buffer may require pulling keys out of journal
entries yet to be written, and quiescing outstanding journal
reservations; we previously added journal->buf_lock for synchronization
with the journal write path.
We also can't put strict bounds on the number of keys in the journal
destined for the write buffer, which means we might overflow the size of
the preallocated buffer and have to reallocate - this introduces a
potentially fatal memory allocation failure. This is something we'll
have to watch for, if it becomes an issue in practice we can do
additional mitigation.
The transaction commit path no longer has to explicitly check if the
write buffer is full and wait on flushing; this is another performance
optimization. Instead, when the btree write buffer is close to full we
change the journal watermark, so that only reservations for journal
reclaim are allowed.
Signed-off-by: Kent Overstreet <[email protected]>
Thanks for your patch, which is the closest match to commit
9e5a6c7797b240f1 ("bcachefs: btree write buffer now slurps keys from
journal") in next-20231121.
fs/bcachefs/btree_write_buffer.c | 507 ++++++++++++++++---------
The committed version has lots of changes, including:
++ for (struct wb_key_ref *n = i + 1; n < min(i + 4,
&darray_top(wb->sorted)); n++)
++ prefetch(&wb->flushing.keys.data[n->idx]);
which requires the inclusion if <linux/prefetch.h>, as reported by
kernel test robot <[email protected]> for arc[1], and by
[email protected] for m68k.
[1]
https://lore.kernel.org/all/[email protected]
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
