linux-kernel - Re: [PATCH 08/16] dm-writecache: use bvec_kmap_local instead of bvec_kmap

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Date:   Tue, 8 Jun 2021 09:30:56 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Geoff Levand <geoff@...radead.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Dongsheng Yang <dongsheng.yang@...ystack.cn>,
        Mike Snitzer <snitzer@...hat.com>,
        Ira Weiny <ira.weiny@...el.com>, dm-devel@...hat.com,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        ceph-devel@...r.kernel.org
Subject: Re: [PATCH 08/16] dm-writecache: use bvec_kmap_local instead of
 bvec_kmap_irq

On 6/8/21 9:05 AM, Christoph Hellwig wrote:
> diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
> index aecc246ade26..93ca454eaca9 100644
> --- a/drivers/md/dm-writecache.c
> +++ b/drivers/md/dm-writecache.c
> @@ -1205,14 +1205,13 @@ static void memcpy_flushcache_optimized(void *dest, void *source, size_t size)
>  static void bio_copy_block(struct dm_writecache *wc, struct bio *bio, void *data)
>  {
>  	void *buf;
> -	unsigned long flags;
>  	unsigned size;
>  	int rw = bio_data_dir(bio);
>  	unsigned remaining_size = wc->block_size;
>  
>  	do {
>  		struct bio_vec bv = bio_iter_iovec(bio, bio->bi_iter);
> -		buf = bvec_kmap_irq(&bv, &flags);
> +		buf = bvec_kmap_local(&bv);
>  		size = bv.bv_len;
>  		if (unlikely(size > remaining_size))
>  			size = remaining_size;
> @@ -1230,7 +1229,7 @@ static void bio_copy_block(struct dm_writecache *wc, struct bio *bio, void *data
>  			memcpy_flushcache_optimized(data, buf, size);
>  		}
>  
> -		bvec_kunmap_irq(buf, &flags);
> +		kunmap_local(buf);
>  
>  		data = (char *)data + size;
>  		remaining_size -= size;

>From one of the functions called by kunmap_local():

unsigned long addr = (unsigned long) vaddr & PAGE_MASK;

This won't work well if bvec->bv_offset >= PAGE_SIZE I assume?

Thanks,

Bart.