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netfs: In readahead, put the folio refs as soon extracted

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netfslib currently defers dropping the ref on the folios it obtains during
readahead to after it has started I/O on the basis that we can do it whilst
we wait for the I/O to complete, but this runs the risk of the I/O
collection racing with this in future.

Furthermore, Matthew Wilcox strongly suggests that the refs should be
dropped immediately, as readahead_folio() does (netfslib is using
__readahead_batch() which doesn't drop the refs).

Fixes: ee4cdf7ba8 ("netfs: Speed up buffered reading")
Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/3771538.1728052438@warthog.procyon.org.uk
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
David Howells 2024-10-04 15:33:58 +01:00 committed by Christian Brauner
parent 8cf0b93919
commit 796a404964
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
3 changed files with 16 additions and 34 deletions
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47
fs/netfs/buffered_read.c
View File

@ -67,7 +67,8 @@ static int netfs_begin_cache_read(struct netfs_io_request *rreq, struct netfs_in
* Decant the list of folios to read into a rolling buffer.
*/
static size_t netfs_load_buffer_from_ra(struct netfs_io_request *rreq,
struct folio_queue *folioq)
struct folio_queue *folioq,
struct folio_batch *put_batch)
{
unsigned int order, nr;
size_t size = 0;
@ -82,6 +83,9 @@ static size_t netfs_load_buffer_from_ra(struct netfs_io_request *rreq,
order = folio_order(folio);
folioq->orders[i] = order;
size += PAGE_SIZE << order;
if (!folio_batch_add(put_batch, folio))
folio_batch_release(put_batch);
}
for (int i = nr; i < folioq_nr_slots(folioq); i++)
@ -120,6 +124,9 @@ static ssize_t netfs_prepare_read_iterator(struct netfs_io_subrequest *subreq)
* that we will need to release later - but we don't want to do
* that until after we've started the I/O.
*/
struct folio_batch put_batch;
folio_batch_init(&put_batch);
while (rreq->submitted < subreq->start + rsize) {
struct folio_queue *tail = rreq->buffer_tail, *new;
size_t added;
@ -132,10 +139,11 @@ static ssize_t netfs_prepare_read_iterator(struct netfs_io_subrequest *subreq)
new->prev = tail;
tail->next = new;
rreq->buffer_tail = new;
added = netfs_load_buffer_from_ra(rreq, new);
added = netfs_load_buffer_from_ra(rreq, new, &put_batch);
rreq->iter.count += added;
rreq->submitted += added;
}
folio_batch_release(&put_batch);
}
subreq->len = rsize;
@ -348,6 +356,7 @@ static int netfs_wait_for_read(struct netfs_io_request *rreq)
static int netfs_prime_buffer(struct netfs_io_request *rreq)
{
struct folio_queue *folioq;
struct folio_batch put_batch;
size_t added;
folioq = kmalloc(sizeof(*folioq), GFP_KERNEL);
@ -360,39 +369,14 @@ static int netfs_prime_buffer(struct netfs_io_request *rreq)
rreq->submitted = rreq->start;
iov_iter_folio_queue(&rreq->iter, ITER_DEST, folioq, 0, 0, 0);
added = netfs_load_buffer_from_ra(rreq, folioq);
folio_batch_init(&put_batch);
added = netfs_load_buffer_from_ra(rreq, folioq, &put_batch);
folio_batch_release(&put_batch);
rreq->iter.count += added;
rreq->submitted += added;
return 0;
}
/*
* Drop the ref on each folio that we inherited from the VM readahead code. We
* still have the folio locks to pin the page until we complete the I/O.
*
* Note that we can't just release the batch in each queue struct as we use the
* occupancy count in other places.
*/
static void netfs_put_ra_refs(struct folio_queue *folioq)
{
struct folio_batch fbatch;
folio_batch_init(&fbatch);
while (folioq) {
for (unsigned int slot = 0; slot < folioq_count(folioq); slot++) {
struct folio *folio = folioq_folio(folioq, slot);
if (!folio)
continue;
trace_netfs_folio(folio, netfs_folio_trace_read_put);
if (!folio_batch_add(&fbatch, folio))
folio_batch_release(&fbatch);
}
folioq = folioq->next;
}
folio_batch_release(&fbatch);
}
/**
* netfs_readahead - Helper to manage a read request
* @ractl: The description of the readahead request
@ -436,9 +420,6 @@ void netfs_readahead(struct readahead_control *ractl)
goto cleanup_free;
netfs_read_to_pagecache(rreq);
/* Release the folio refs whilst we're waiting for the I/O. */
netfs_put_ra_refs(rreq->buffer);
netfs_put_request(rreq, true, netfs_rreq_trace_put_return);
return;

2
fs/netfs/read_collect.c
View File

@ -77,6 +77,8 @@ static void netfs_unlock_read_folio(struct netfs_io_subrequest *subreq,
folio_unlock(folio);
}
}
folioq_clear(folioq, slot);
}
/*

1
include/trace/events/netfs.h
View File

@ -172,7 +172,6 @@
EM(netfs_folio_trace_read, "read") \
EM(netfs_folio_trace_read_done, "read-done") \
EM(netfs_folio_trace_read_gaps, "read-gaps") \
EM(netfs_folio_trace_read_put, "read-put") \
EM(netfs_folio_trace_read_unlock, "read-unlock") \
EM(netfs_folio_trace_redirtied, "redirtied") \
EM(netfs_folio_trace_store, "store") \