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NFSv4/flexfiles: honor FF_FLAGS_NO_IO_THRU_MDS in pg_get_mirror_count_write

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The FF_FLAGS_NO_IO_THRU_MDS flag lives on each lseg, so any fallback
decision made when there is no current lseg (e.g. between LAYOUTRETURN
and the next LAYOUTGET) cannot run the per-lseg check.

Introduce a sticky hdr-level ditto for FF_FLAGS_NO_IO_THRU_MDS in
struct nfs4_flexfile_layout::flags (NFS4_FF_HDR_NO_IO_THRU_MDS bit),
set whenever ff_layout_alloc_lseg() parses an lseg with the flag.  The
bit is never cleared for the lifetime of the layout hdr; the server is
assumed to be consistent in its no-fallback policy per file.
kzalloc() in ff_layout_alloc_layout_hdr() zero-initializes the field.

Use the new ff_layout_hdr_no_fallback_to_mds() helper to gate
ff_layout_pg_get_mirror_count_write(): when pnfs_update_layout() returns
NULL (e.g. NFS_LAYOUT_BULK_RECALL, pnfs_layout_io_test_failed,
pnfs_layoutgets_blocked) the existing code unconditionally calls
nfs_pageio_reset_write_mds().  This is a source of unwanted WRITE to
MDS.  Fix it by checking NFS4_FF_HDR_NO_IO_THRU_MDS bit, and if set
surface -EAGAIN instead; the writepage-side caller (nfs_do_writepage()
for buffered, nfs_direct_write_reschedule() for O_DIRECT) then
redirties the request so writeback retries via pNFS.

Fixes: 260074cd84 ("pNFS/flexfiles: Add support for FF_FLAGS_NO_IO_THRU_MDS")
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@hammerspace.com>
This commit is contained in:
Mike Snitzer
2026-06-04 16:24:03 -04:00
committed by Anna Schumaker
parent 7a375cafc1
commit 1d62e659c0
2 changed files with 29 additions and 0 deletions
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13
fs/nfs/flexfilelayout/flexfilelayout.c
View File

@@ -636,6 +636,9 @@ ff_layout_alloc_lseg(struct pnfs_layout_hdr *lh,
if (!p)
goto out_sort_mirrors;
fls->flags = be32_to_cpup(p);
if (fls->flags & FF_FLAGS_NO_IO_THRU_MDS)
set_bit(NFS4_FF_HDR_NO_IO_THRU_MDS,
&FF_LAYOUT_FROM_HDR(lh)->flags);
p = xdr_inline_decode(&stream, 4);
if (!p)
@@ -1185,6 +1188,16 @@ ff_layout_pg_get_mirror_count_write(struct nfs_pageio_descriptor *pgio,
0, NFS4_MAX_UINT64, IOMODE_RW,
NFS_I(pgio->pg_inode)->layout,
pgio->pg_lseg);
if (NFS_I(pgio->pg_inode)->layout &&
ff_layout_hdr_no_fallback_to_mds(NFS_I(pgio->pg_inode)->layout)) {
/*
* FF_FLAGS_NO_IO_THRU_MDS: no current lseg but the server's
* policy forbids MDS fallback. Surface -EAGAIN so writeback
* retries rather than silently issuing the WRITE via MDS.
*/
pgio->pg_error = -EAGAIN;
goto out;
}
/* no lseg means that pnfs is not in use, so no mirroring here */
nfs_pageio_reset_write_mds(pgio);
out:

16
fs/nfs/flexfilelayout/flexfilelayout.h
View File

@@ -112,12 +112,16 @@ struct nfs4_ff_layout_segment {
struct nfs4_ff_layout_mirror *mirror_array[] __counted_by(mirror_array_cnt);
};
/* nfs4_flexfile_layout::flags bit indices */
#define NFS4_FF_HDR_NO_IO_THRU_MDS 0 /* any lseg has had FF_FLAGS_NO_IO_THRU_MDS */
struct nfs4_flexfile_layout {
struct pnfs_layout_hdr generic_hdr;
struct pnfs_ds_commit_info commit_info;
struct list_head mirrors;
struct list_head error_list; /* nfs4_ff_layout_ds_err */
ktime_t last_report_time; /* Layoutstat report times */
unsigned long flags;
};
struct nfs4_flexfile_layoutreturn_args {
@@ -184,6 +188,18 @@ ff_layout_no_fallback_to_mds(struct pnfs_layout_segment *lseg)
return FF_LAYOUT_LSEG(lseg)->flags & FF_FLAGS_NO_IO_THRU_MDS;
}
/*
* Sticky hdr-level mirror of FF_FLAGS_NO_IO_THRU_MDS so callers that have
* no current lseg (e.g. between LAYOUTRETURN and the next LAYOUTGET) can
* still honor the no-MDS-fallback policy.
*/
static inline bool
ff_layout_hdr_no_fallback_to_mds(struct pnfs_layout_hdr *lo)
{
return test_bit(NFS4_FF_HDR_NO_IO_THRU_MDS,
&FF_LAYOUT_FROM_HDR(lo)->flags);
}
static inline bool
ff_layout_no_read_on_rw(struct pnfs_layout_segment *lseg)
{