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netfs: Make netfs_read_folio() handle streaming-write pages

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netfs_read_folio() needs to handle partially-valid pages that are marked
dirty, but not uptodate in the event that someone tries to read a page was
used to cache data by a streaming write.

In such a case, make netfs_read_folio() set up a bvec iterator that points
to the parts of the folio that need filling and to a sink page for the data
that should be discarded and use that instead of i_pages as the iterator to
be written to.

This requires netfs_rreq_unlock_folios() to convert the page into a normal
dirty uptodate page, getting rid of the partial write record and bumping
the group pointer over to folio->private.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
This commit is contained in:
David Howells 2023-10-02 12:51:19 +01:00
parent c38f4e96e6
commit 7f84a7b989
2 changed files with 60 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
fs/netfs/buffered_read.c
View File

@ -16,6 +16,7 @@
void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
{
struct netfs_io_subrequest *subreq;
struct netfs_folio *finfo;
struct folio *folio;
pgoff_t start_page = rreq->start / PAGE_SIZE;
pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
@ -87,6 +88,15 @@ void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
if (!pg_failed) {
flush_dcache_folio(folio);
finfo = netfs_folio_info(folio);
if (finfo) {
trace_netfs_folio(folio, netfs_folio_trace_filled_gaps);
if (finfo->netfs_group)
folio_change_private(folio, finfo->netfs_group);
else
folio_detach_private(folio);
kfree(finfo);
}
folio_mark_uptodate(folio);
}
@ -239,6 +249,7 @@ int netfs_read_folio(struct file *file, struct folio *folio)
struct address_space *mapping = folio_file_mapping(folio);
struct netfs_io_request *rreq;
struct netfs_inode *ctx = netfs_inode(mapping->host);
struct folio *sink = NULL;
int ret;
_enter("%lx", folio_index(folio));
@ -259,12 +270,56 @@ int netfs_read_folio(struct file *file, struct folio *folio)
trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
/* Set up the output buffer */
iov_iter_xarray(&rreq->iter, ITER_DEST, &mapping->i_pages,
rreq->start, rreq->len);
if (folio_test_dirty(folio)) {
/* Handle someone trying to read from an unflushed streaming
* write. We fiddle the buffer so that a gap at the beginning
* and/or a gap at the end get copied to, but the middle is
* discarded.
*/
struct netfs_folio *finfo = netfs_folio_info(folio);
struct bio_vec *bvec;
unsigned int from = finfo->dirty_offset;
unsigned int to = from + finfo->dirty_len;
unsigned int off = 0, i = 0;
size_t flen = folio_size(folio);
size_t nr_bvec = flen / PAGE_SIZE + 2;
size_t part;
ret = -ENOMEM;
bvec = kmalloc_array(nr_bvec, sizeof(*bvec), GFP_KERNEL);
if (!bvec)
goto discard;
sink = folio_alloc(GFP_KERNEL, 0);
if (!sink)
goto discard;
trace_netfs_folio(folio, netfs_folio_trace_read_gaps);
rreq->direct_bv = bvec;
rreq->direct_bv_count = nr_bvec;
if (from > 0) {
bvec_set_folio(&bvec[i++], folio, from, 0);
off = from;
}
while (off < to) {
part = min_t(size_t, to - off, PAGE_SIZE);
bvec_set_folio(&bvec[i++], sink, part, 0);
off += part;
}
if (to < flen)
bvec_set_folio(&bvec[i++], folio, flen - to, to);
iov_iter_bvec(&rreq->iter, ITER_DEST, bvec, i, rreq->len);
} else {
iov_iter_xarray(&rreq->iter, ITER_DEST, &mapping->i_pages,
rreq->start, rreq->len);
}
ret = netfs_begin_read(rreq, true);
if (sink)
folio_put(sink);
netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
return ret;
return ret < 0 ? ret : 0;
discard:
netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);

2
include/trace/events/netfs.h
View File

@ -118,9 +118,11 @@
EM(netfs_folio_trace_clear_g, "clear-g") \
EM(netfs_folio_trace_copy_to_cache, "copy") \
EM(netfs_folio_trace_end_copy, "end-copy") \
EM(netfs_folio_trace_filled_gaps, "filled-gaps") \
EM(netfs_folio_trace_kill, "kill") \
EM(netfs_folio_trace_mkwrite, "mkwrite") \
EM(netfs_folio_trace_mkwrite_plus, "mkwrite+") \
EM(netfs_folio_trace_read_gaps, "read-gaps") \
EM(netfs_folio_trace_redirty, "redirty") \
EM(netfs_folio_trace_redirtied, "redirtied") \
EM(netfs_folio_trace_store, "store") \