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

Darrick J. Wong
2025-02-06T21:54:23Z

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@oracle.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
> > >
> > >
>
>