Re: [PATCH] fs: make sure to invalidate pages if we fall back on buffered reads

[Jeff Moyer]

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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