* [PATCH v2 1/2] filemap: Add a helper for filesystems implementing dropbehind
2025-08-12 21:40 [PATCH v2 0/2] Initial NFS client support for RWF_DONTCACHE Trond Myklebust
@ 2025-08-12 21:40 ` Trond Myklebust
2025-08-12 21:40 ` [PATCH v2 2/2] NFS: Enable the RWF_DONTCACHE flag for the NFS client Trond Myklebust
1 sibling, 0 replies; 3+ messages in thread
From: Trond Myklebust @ 2025-08-12 21:40 UTC (permalink / raw)
To: linux-nfs; +Cc: linux-fsdevel, Mike Snitzer
From: Trond Myklebust <trond.myklebust@hammerspace.com>
Add a helper to allow filesystems to attempt to free the 'dropbehind'
folio.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Link: https://lore.kernel.org/all/5588a06f6d5a2cf6746828e2d36e7ada668b1739.1745381692.git.trond.myklebust@hammerspace.com/
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
---
include/linux/pagemap.h | 1 +
mm/filemap.c | 16 ++++++++++++++++
2 files changed, 17 insertions(+)
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 12a12dae727d..201b7c6f6441 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1221,6 +1221,7 @@ void folio_wait_writeback(struct folio *folio);
int folio_wait_writeback_killable(struct folio *folio);
void end_page_writeback(struct page *page);
void folio_end_writeback(struct folio *folio);
+void folio_end_dropbehind(struct folio *folio);
void folio_wait_stable(struct folio *folio);
void __folio_mark_dirty(struct folio *folio, struct address_space *, int warn);
void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb);
diff --git a/mm/filemap.c b/mm/filemap.c
index 751838ef05e5..9878ab702e54 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1603,6 +1603,22 @@ static void filemap_end_dropbehind(struct folio *folio)
folio_unmap_invalidate(mapping, folio, 0);
}
+/*
+ * Helper for filesystems that want to implement dropbehind, and that
+ * need to keep the folio around after folio_end_writeback, e.g. due to
+ * the need to first commit NFS stable writes.
+ */
+void folio_end_dropbehind(struct folio *folio)
+{
+ if (folio_trylock(folio)) {
+ if (folio->mapping && !folio_test_dirty(folio) &&
+ !folio_test_writeback(folio))
+ folio_unmap_invalidate(folio->mapping, folio, 0);
+ folio_unlock(folio);
+ }
+}
+EXPORT_SYMBOL(folio_end_dropbehind);
+
/*
* If folio was marked as dropbehind, then pages should be dropped when writeback
* completes. Do that now. If we fail, it's likely because of a big folio -
--
2.50.1
^ permalink raw reply related [flat|nested] 3+ messages in thread* [PATCH v2 2/2] NFS: Enable the RWF_DONTCACHE flag for the NFS client
2025-08-12 21:40 [PATCH v2 0/2] Initial NFS client support for RWF_DONTCACHE Trond Myklebust
2025-08-12 21:40 ` [PATCH v2 1/2] filemap: Add a helper for filesystems implementing dropbehind Trond Myklebust
@ 2025-08-12 21:40 ` Trond Myklebust
1 sibling, 0 replies; 3+ messages in thread
From: Trond Myklebust @ 2025-08-12 21:40 UTC (permalink / raw)
To: linux-nfs; +Cc: linux-fsdevel, Mike Snitzer
From: Trond Myklebust <trond.myklebust@hammerspace.com>
While the NFS readahead code has no problems using the generic code to
manage the dropbehind behaviour enabled by RWF_DONTCACHE, the write code
needs to deal with the fact that NFS writeback uses a 2 step process
(UNSTABLE write followed by COMMIT).
This commit replaces the use of the folio dropbehind flag with a local
NFS request flag that triggers the dropbehind behaviour once the data
has been written to stable storage.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Link: https://lore.kernel.org/all/ec165b304a7b56d1fa4c6c2b1ad1c04d4dcbd3f6.1745381692.git.trond.myklebust@hammerspace.com/
Reviewed-by: Mike Snitzer <snitzer@kernel.org>
---
fs/nfs/file.c | 7 +++----
fs/nfs/nfs4file.c | 2 ++
fs/nfs/write.c | 12 +++++++++++-
include/linux/nfs_page.h | 1 +
4 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 86e36c630f09..fffb536bfcdd 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -348,7 +348,6 @@ static int nfs_write_begin(const struct kiocb *iocb,
loff_t pos, unsigned len, struct folio **foliop,
void **fsdata)
{
- fgf_t fgp = FGP_WRITEBEGIN;
struct folio *folio;
struct file *file = iocb->ki_filp;
int once_thru = 0;
@@ -357,10 +356,8 @@ static int nfs_write_begin(const struct kiocb *iocb,
dfprintk(PAGECACHE, "NFS: write_begin(%pD2(%lu), %u@%lld)\n",
file, mapping->host->i_ino, len, (long long) pos);
- fgp |= fgf_set_order(len);
start:
- folio = __filemap_get_folio(mapping, pos >> PAGE_SHIFT, fgp,
- mapping_gfp_mask(mapping));
+ folio = write_begin_get_folio(iocb, mapping, pos >> PAGE_SHIFT, len);
if (IS_ERR(folio))
return PTR_ERR(folio);
*foliop = folio;
@@ -915,5 +912,7 @@ const struct file_operations nfs_file_operations = {
.splice_write = iter_file_splice_write,
.check_flags = nfs_check_flags,
.setlease = simple_nosetlease,
+
+ .fop_flags = FOP_DONTCACHE,
};
EXPORT_SYMBOL_GPL(nfs_file_operations);
diff --git a/fs/nfs/nfs4file.c b/fs/nfs/nfs4file.c
index 1d6b5f4230c9..70f6887ded0e 100644
--- a/fs/nfs/nfs4file.c
+++ b/fs/nfs/nfs4file.c
@@ -454,4 +454,6 @@ const struct file_operations nfs4_file_operations = {
#else
.llseek = nfs_file_llseek,
#endif
+
+ .fop_flags = FOP_DONTCACHE,
};
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index fa5c41d0989a..e6b1f69058cf 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -359,8 +359,12 @@ static void nfs_folio_end_writeback(struct folio *folio)
static void nfs_page_end_writeback(struct nfs_page *req)
{
if (nfs_page_group_sync_on_bit(req, PG_WB_END)) {
+ struct folio *folio = nfs_page_to_folio(req);
+
+ if (folio_test_clear_dropbehind(folio))
+ set_bit(PG_DROPBEHIND, &req->wb_flags);
nfs_unlock_request(req);
- nfs_folio_end_writeback(nfs_page_to_folio(req));
+ nfs_folio_end_writeback(folio);
} else
nfs_unlock_request(req);
}
@@ -797,6 +801,9 @@ static void nfs_inode_remove_request(struct nfs_page *req)
clear_bit(PG_MAPPED, &req->wb_head->wb_flags);
}
spin_unlock(&mapping->i_private_lock);
+
+ if (test_bit(PG_DROPBEHIND, &req->wb_flags))
+ folio_end_dropbehind(folio);
}
if (test_and_clear_bit(PG_INODE_REF, &req->wb_flags)) {
@@ -2077,6 +2084,7 @@ int nfs_wb_folio(struct inode *inode, struct folio *folio)
.range_start = range_start,
.range_end = range_start + len - 1,
};
+ bool dropbehind = folio_test_clear_dropbehind(folio);
int ret;
trace_nfs_writeback_folio(inode, range_start, len);
@@ -2097,6 +2105,8 @@ int nfs_wb_folio(struct inode *inode, struct folio *folio)
goto out_error;
}
out_error:
+ if (dropbehind)
+ folio_set_dropbehind(folio);
trace_nfs_writeback_folio_done(inode, range_start, len, ret);
return ret;
}
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index 169b4ae30ff4..1a017b5b476f 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -37,6 +37,7 @@ enum {
PG_REMOVE, /* page group sync bit in write path */
PG_CONTENDED1, /* Is someone waiting for a lock? */
PG_CONTENDED2, /* Is someone waiting for a lock? */
+ PG_DROPBEHIND, /* Implement RWF_DONTCACHE */
};
struct nfs_inode;
--
2.50.1
^ permalink raw reply related [flat|nested] 3+ messages in thread