On Wed, Jul 17, 2024 at 4:24 PM Yu Ma <yu.ma@xxxxxxxxx> wrote: > > Skip 2-levels searching via find_next_zero_bit() when there is free slot in the > word contains next_fd, as: > (1) next_fd indicates the lower bound for the first free fd. > (2) There is fast path inside of find_next_zero_bit() when size<=64 to speed up > searching. this is stale -- now the fast path searches up to 64 fds in the lower bitmap > (3) After fdt is expanded (the bitmap size doubled for each time of expansion), > it would never be shrunk. The search size increases but there are few open fds > available here. > > This fast path is proposed by Mateusz Guzik <mjguzik@xxxxxxxxx>, and agreed by > Jan Kara <jack@xxxxxxx>, which is more generic and scalable than previous > versions. I think this paragraph is droppable. You already got an ack from Jan below, so stating he agrees with the patch is redundant. As for me I don't think this warrants mentioning. Just remove it, perhaps Christian will be willing to massage it by himself to avoid another series posting. > And on top of patch 1 and 2, it improves pts/blogbench-1.1.0 read by > 8% and write by 4% on Intel ICX 160 cores configuration with v6.10-rc7. > > Reviewed-by: Jan Kara <jack@xxxxxxx> > Reviewed-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> > Signed-off-by: Yu Ma <yu.ma@xxxxxxxxx> > --- > fs/file.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/fs/file.c b/fs/file.c > index 1be2a5bcc7c4..729c07a4fc28 100644 > --- a/fs/file.c > +++ b/fs/file.c > @@ -491,6 +491,15 @@ static unsigned int find_next_fd(struct fdtable *fdt, unsigned int start) > unsigned int maxfd = fdt->max_fds; /* always multiple of BITS_PER_LONG */ > unsigned int maxbit = maxfd / BITS_PER_LONG; > unsigned int bitbit = start / BITS_PER_LONG; > + unsigned int bit; > + > + /* > + * Try to avoid looking at the second level bitmap > + */ > + bit = find_next_zero_bit(&fdt->open_fds[bitbit], BITS_PER_LONG, > + start & (BITS_PER_LONG - 1)); > + if (bit < BITS_PER_LONG) > + return bit + bitbit * BITS_PER_LONG; > > bitbit = find_next_zero_bit(fdt->full_fds_bits, maxbit, bitbit) * BITS_PER_LONG; > if (bitbit >= maxfd) > -- > 2.43.0 > -- Mateusz Guzik <mjguzik gmail.com>
