Josef Bacik <josef@xxxxxxxxxx> writes:
> Since BTRFS can fallback on buffered reads after having done some direct reads,
> we need to make sure to invalidate any pages that we may have read by doing
> buffered IO. This shouldn't have shown up as a visible user problem, it's just
> for correctness sake. Thanks,
This looks right to me. You definitely don't want to fill up the page
cache from direct I/O.
Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxx>
> ---
> mm/filemap.c | 9 ++++++++-
> 1 files changed, 8 insertions(+), 1 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 829ac9c..ca5aba9 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1266,6 +1266,7 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
> unsigned long seg = 0;
> size_t count;
> loff_t *ppos = &iocb->ki_pos;
> + bool invalidate = false;
>
> count = 0;
> retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
> @@ -1291,7 +1292,8 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
> iov, pos, nr_segs);
> }
> if (retval > 0) {
> - *ppos = pos + retval;
> + pos += retval;
> + *ppos = pos;
> count -= retval;
> }
>
> @@ -1307,6 +1309,7 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
> file_accessed(filp);
> goto out;
> }
> + invalidate = true;
> }
> }
>
> @@ -1343,6 +1346,10 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
> if (desc.count > 0)
> break;
> }
> + if (invalidate && retval > 0)
> + invalidate_mapping_pages(filp->f_mapping,
> + pos >> PAGE_CACHE_SHIFT,
> + (*ppos - 1) >> PAGE_CACHE_SHIFT);
> out:
> return retval;
> }
--
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