linux-kernel - Re: [PATCH RFC 10/10] xfs: Allow block allocator to take an alignment hint

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Message-ID: <20250206215422.GZ21808@frogsfrogsfrogs>
Date: Thu, 6 Feb 2025 13:54:22 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: John Garry <john.g.garry@...cle.com>
Cc: brauner@...nel.org, cem@...nel.org, dchinner@...hat.com, hch@....de,
	linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, ojaswin@...ux.ibm.com,
	ritesh.list@...il.com, martin.petersen@...cle.com
Subject: Re: [PATCH RFC 10/10] xfs: Allow block allocator to take an
 alignment hint

On Thu, Feb 06, 2025 at 08:10:24AM +0000, John Garry wrote:
> On 05/02/2025 19:20, Darrick J. Wong wrote:
> > On Tue, Feb 04, 2025 at 12:01:27PM +0000, John Garry wrote:
> > > When issuing an atomic write by the CoW method, give the block allocator a
> > > hint to naturally align the data blocks.
> > > 
> > > This means that we have a better chance to issuing the atomic write via
> > > HW offload next time.
> > > 
> > > Signed-off-by: John Garry <john.g.garry@...cle.com>
> > > ---
> > >   fs/xfs/libxfs/xfs_bmap.c | 7 ++++++-
> > >   fs/xfs/libxfs/xfs_bmap.h | 6 +++++-
> > >   fs/xfs/xfs_reflink.c     | 8 ++++++--
> > >   3 files changed, 17 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> > > index 40ad22fb808b..7a3910018dee 100644
> > > --- a/fs/xfs/libxfs/xfs_bmap.c
> > > +++ b/fs/xfs/libxfs/xfs_bmap.c
> > > @@ -3454,6 +3454,12 @@ xfs_bmap_compute_alignments(
> > >   		align = xfs_get_cowextsz_hint(ap->ip);
> > >   	else if (ap->datatype & XFS_ALLOC_USERDATA)
> > >   		align = xfs_get_extsz_hint(ap->ip);
> > > +
> > > +	if (align > 1 && ap->flags & XFS_BMAPI_NALIGN)
> > > +		args->alignment = align;
> > > +	else
> > > +		args->alignment = 1;
> > > +
> > >   	if (align) {
> > >   		if (xfs_bmap_extsize_align(mp, &ap->got, &ap->prev, align, 0,
> > >   					ap->eof, 0, ap->conv, &ap->offset,
> > > @@ -3781,7 +3787,6 @@ xfs_bmap_btalloc(
> > >   		.wasdel		= ap->wasdel,
> > >   		.resv		= XFS_AG_RESV_NONE,
> > >   		.datatype	= ap->datatype,
> > > -		.alignment	= 1,
> > >   		.minalignslop	= 0,
> > >   	};
> > >   	xfs_fileoff_t		orig_offset;
> > > diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
> > > index 4b721d935994..d68b594c3fa2 100644
> > > --- a/fs/xfs/libxfs/xfs_bmap.h
> > > +++ b/fs/xfs/libxfs/xfs_bmap.h
> > > @@ -87,6 +87,9 @@ struct xfs_bmalloca {
> > >   /* Do not update the rmap btree.  Used for reconstructing bmbt from rmapbt. */
> > >   #define XFS_BMAPI_NORMAP	(1u << 10)
> > > +/* Try to naturally align allocations */
> > > +#define XFS_BMAPI_NALIGN	(1u << 11)
> > > +
> > >   #define XFS_BMAPI_FLAGS \
> > >   	{ XFS_BMAPI_ENTIRE,	"ENTIRE" }, \
> > >   	{ XFS_BMAPI_METADATA,	"METADATA" }, \
> > > @@ -98,7 +101,8 @@ struct xfs_bmalloca {
> > >   	{ XFS_BMAPI_REMAP,	"REMAP" }, \
> > >   	{ XFS_BMAPI_COWFORK,	"COWFORK" }, \
> > >   	{ XFS_BMAPI_NODISCARD,	"NODISCARD" }, \
> > > -	{ XFS_BMAPI_NORMAP,	"NORMAP" }
> > > +	{ XFS_BMAPI_NORMAP,	"NORMAP" },\
> > > +	{ XFS_BMAPI_NALIGN,	"NALIGN" }
> > 
> > Tihs isn't really "naturally" aligned, is it?  It really means "try to
> > align allocations to the extent size hint", which isn't required to be a
> > power of two.
> 
> Sure, so I would expect that the user will set extsize/cowextsize according
> to the size what we want to do atomics for, and we can align to that. I
> don't think that it makes a difference that either extsize isn't mandated to
> be a power-of-2.
> 
> So then I should rename to XFS_BMAPI_EXTSZALIGN or something like that - ok?

Yep.

--D

> Thanks,
> John
> 
> 
> > 
> > --D
> > 
> > >   static inline int xfs_bmapi_aflag(int w)
> > > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> > > index 60c986300faa..198fb5372f10 100644
> > > --- a/fs/xfs/xfs_reflink.c
> > > +++ b/fs/xfs/xfs_reflink.c
> > > @@ -445,6 +445,11 @@ xfs_reflink_fill_cow_hole(
> > >   	int			nimaps;
> > >   	int			error;
> > >   	bool			found;
> > > +	uint32_t		bmapi_flags = XFS_BMAPI_COWFORK |
> > > +					XFS_BMAPI_PREALLOC;
> > > +
> > > +	if (atomic)
> > > +		bmapi_flags |= XFS_BMAPI_NALIGN;
> > >   	resaligned = xfs_aligned_fsb_count(imap->br_startoff,
> > >   		imap->br_blockcount, xfs_get_cowextsz_hint(ip));
> > > @@ -478,8 +483,7 @@ xfs_reflink_fill_cow_hole(
> > >   	/* Allocate the entire reservation as unwritten blocks. */
> > >   	nimaps = 1;
> > >   	error = xfs_bmapi_write(tp, ip, imap->br_startoff, imap->br_blockcount,
> > > -			XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC, 0, cmap,
> > > -			&nimaps);
> > > +			bmapi_flags, 0, cmap, &nimaps);
> > >   	if (error)
> > >   		goto out_trans_cancel;
> > > -- 
> > > 2.31.1
> > > 
> > > 
> 
>