linux-ext4 - Re: [PATCH 14/17] iomap: make buffered writes work with RWF

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Message-ID: <Z1p5my4wynAW_Vc3@infradead.org>
Date: Wed, 11 Dec 2024 21:50:19 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, hannes@...xchg.org,
	clm@...a.com, linux-kernel@...r.kernel.org, willy@...radead.org,
	kirill@...temov.name, linux-btrfs@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
	bfoster@...hat.com
Subject: Re: [PATCH 14/17] iomap: make buffered writes work with RWF_UNCACHED

On Thu, Nov 14, 2024 at 08:25:18AM -0700, Jens Axboe wrote:
> +	if (iocb->ki_flags & IOCB_UNCACHED)
> +		iter.flags |= IOMAP_UNCACHED;
>  
> -	while ((ret = iomap_iter(&iter, ops)) > 0)
> +	while ((ret = iomap_iter(&iter, ops)) > 0) {
> +		if (iocb->ki_flags & IOCB_UNCACHED)
> +			iter.iomap.flags |= IOMAP_F_UNCACHED;

iomap.flags and the IOMAP_F_* namespace is used to communicate flags
from the file system to the iomap core, so this looks wrong.

>  	size_t poff = offset_in_folio(folio, pos);
>  	int error;
>  
> +	if (folio_test_uncached(folio))
> +		wpc->iomap.flags |= IOMAP_F_UNCACHED;

I guess this is what actually makes it work.  Note that with the iomap
zoned series I posted yesteday things change a bit here in that the flags
in the wpc are decouple from the iomap flags, and this would now become
a wpc only flag as it isn't really a fs to iomap cummunication, but
based on iomap / page cache state.