[PATCH v11 27/36] netfs: Build a list of regions undergoing writeback
David Howells
dhowells at redhat.com
Wed Sep 2 10:33:39 PDT 2026
Build a linked list of the regions of file position that are involved in a
writeback whilst processing the folios to be written back. These will be
used in a subsequent patch to work out which folios need unlocking rather
than walking the bvecq list of folios.
This will mean that the folio list need not be maintained as a single list
of folios, but can instead be made into multiple lists and have various
roundings applied to it - and can be ignored by the collector, except when
various pins are pulled out of it by subrequest cleanup.
Signed-off-by: David Howells <dhowells at redhat.com>
cc: Paulo Alcantara <pc at manguebit.org>
cc: Matthew Wilcox <willy at infradead.org>
cc: Christoph Hellwig <hch at infradead.org>
cc: netfs at lists.linux.dev
cc: linux-fsdevel at vger.kernel.org
---
fs/netfs/internal.h | 1 +
fs/netfs/main.c | 7 +++++++
fs/netfs/objects.c | 7 +++++++
fs/netfs/write_issue.c | 20 ++++++++++++++++++++
include/linux/netfs.h | 12 ++++++++++++
5 files changed, 47 insertions(+)
diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 8d91748ae257..e6e768ad9648 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -44,6 +44,7 @@ extern struct list_head netfs_io_requests;
extern spinlock_t netfs_proc_lock;
extern mempool_t netfs_request_pool;
extern mempool_t netfs_subrequest_pool;
+extern mempool_t netfs_writeback_pool;
extern mempool_t netfs_bvecq_pool;
#ifdef CONFIG_PROC_FS
diff --git a/fs/netfs/main.c b/fs/netfs/main.c
index 5d8b87f71888..b8da5e85cc67 100644
--- a/fs/netfs/main.c
+++ b/fs/netfs/main.c
@@ -28,6 +28,7 @@ static struct kmem_cache *netfs_request_slab;
static struct kmem_cache *netfs_subrequest_slab;
mempool_t netfs_request_pool;
mempool_t netfs_subrequest_pool;
+mempool_t netfs_writeback_pool;
mempool_t netfs_bvecq_pool;
#ifdef CONFIG_PROC_FS
@@ -110,6 +111,9 @@ static int __init netfs_init(void)
if (mempool_init_kmalloc_pool(&netfs_bvecq_pool, 100, BVECQ_STD_SIZE) < 0)
goto error_bvecq_pool;
+ if (mempool_init_kmalloc_pool(&netfs_writeback_pool, 100,
+ sizeof(struct netfs_writeback)) < 0)
+ goto error_writeback_pool;
netfs_request_slab = kmem_cache_create("netfs_request",
sizeof(struct netfs_io_request), 0,
@@ -163,6 +167,8 @@ static int __init netfs_init(void)
error_reqpool:
kmem_cache_destroy(netfs_request_slab);
error_req:
+ mempool_exit(&netfs_writeback_pool);
+error_writeback_pool:
mempool_exit(&netfs_bvecq_pool);
error_bvecq_pool:
return ret;
@@ -177,6 +183,7 @@ static void __exit netfs_exit(void)
kmem_cache_destroy(netfs_subrequest_slab);
mempool_exit(&netfs_request_pool);
kmem_cache_destroy(netfs_request_slab);
+ mempool_exit(&netfs_writeback_pool);
mempool_exit(&netfs_bvecq_pool);
}
module_exit(netfs_exit);
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index 740971955198..763be168d6b1 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -151,6 +151,13 @@ static void netfs_deinit_request(struct netfs_io_request *rreq)
bvecq_pos_unset(&rreq->dispatch_cursor);
bvecq_pos_unset(&rreq->collect_cursor);
bvecq_put(rreq->spare);
+ while (rreq->writebacks) {
+ struct netfs_writeback *wback = rreq->writebacks;
+
+ rreq->writebacks = wback->next;
+ mempool_free(wback, &netfs_bvecq_pool);
+
+ }
if (atomic_dec_and_test(&ictx->io_count))
wake_up_var(&ictx->io_count);
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 60a417026e10..ace790b127ca 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -335,6 +335,7 @@ static int netfs_write_folio(struct netfs_io_request *wreq,
struct netfs_io_stream *upload = &wreq->io_streams[0];
struct netfs_io_stream *cache = &wreq->io_streams[1];
struct netfs_io_stream *stream;
+ struct netfs_writeback *wback;
struct netfs_group *fgroup; /* TODO: Use this with ceph */
struct netfs_folio *finfo;
struct bvecq *queue = wreq->load_cursor.bvecq;
@@ -433,6 +434,25 @@ static int netfs_write_folio(struct netfs_io_request *wreq,
folio_start_writeback(folio);
folio_unlock(folio);
+ /* Keep track of what we will need to unlock. */
+ wback = wreq->writebacks_tail;
+ if (!wback || fpos != wback->start + wback->len || wback->len > LONG_MAX) {
+ wback = mempool_alloc(&netfs_writeback_pool, wreq->gfp);
+ wback->next = NULL;
+ wback->start = fpos;
+ wback->len = fsize;
+
+ if (wreq->writebacks)
+ /* Order write of next after last write of len in old tail. */
+ smp_store_release(&wreq->writebacks_tail->next, wback);
+ else
+ wreq->writebacks = wback;
+ wreq->writebacks_tail = wback;
+ } else {
+ /* Order update of len after setting pointer. */
+ smp_store_release(&wback->len, wback->len + fsize);
+ }
+
if (fgroup == NETFS_FOLIO_COPY_TO_CACHE) {
if (!cache->avail) {
trace_netfs_folio(folio, netfs_folio_trace_cancel_copy);
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 8d5f548a77c3..70eb32f073f8 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -134,6 +134,16 @@ enum netfs_cache_collect {
NETFS_CACHE_COLLECT_WRITE_CANCEL, /* Currently collecting cancelled writes */
};
+/*
+ * Record of a contiguous region undergoing writeback. The tail region (ie. if
+ * next is NULL) may be extended dynamically.
+ */
+struct netfs_writeback {
+ struct netfs_writeback *next; /* Next extent in list */
+ uoff_t start; /* Start position */
+ size_t len; /* Total size (can increase) */
+};
+
/*
* Stream of I/O subrequests going to a particular destination, such as the
* server or the local cache. This is mainly intended for writing where we may
@@ -249,6 +259,8 @@ struct netfs_io_request {
#endif
struct netfs_io_stream io_streams[2]; /* Streams of parallel I/O operations */
#define NR_IO_STREAMS 2 //wreq->nr_io_streams
+ struct netfs_writeback *writebacks; /* List of regions undergoing writeback */
+ struct netfs_writeback *writebacks_tail; /* Tail of region list */
struct netfs_group *group; /* Writeback group being written back */
struct bvecq *spare; /* Advance allocation of bvecq */
struct bvecq_pos load_cursor; /* Point at which new folios are loaded in */
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