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cifs: Fix read-performance regression by dropping readahead expansion

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cifs_expand_read() is causing a performance regression of around 30% by
causing extra pagecache to be allocated for an inode in the readahead path
before we begin actually dispatching RPC requests, thereby delaying the
actual I/O.  The expansion is sized according to the rsize parameter, which
seems to be 4MiB on my test system; this is a big step up from the first
requests made by the fio test program.

Simple repro (look at read bandwidth number):
     fio --name=writetest --filename=/xfstest.test/foo --time_based --runtime=60 --size=16M --numjobs=1 --rw=read

Fix this by removing cifs_expand_readahead().  Readahead expansion is
mostly useful for when we're using the local cache if the local cache has a
block size greater than PAGE_SIZE, so we can dispense with it when not
caching.

Fixes: 69c3c023af ("cifs: Implement netfslib hooks")
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
David Howells 2024-07-02 15:50:09 +01:00 committed by Steve French
parent 22a40d14b5
commit 08f70c0a93
1 changed files with 0 additions and 30 deletions
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30
fs/smb/client/file.c
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@ -245,35 +245,6 @@ static int cifs_init_request(struct netfs_io_request *rreq, struct file *file)
return 0;
}
/*
* Expand the size of a readahead to the size of the rsize, if at least as
* large as a page, allowing for the possibility that rsize is not pow-2
* aligned.
*/
static void cifs_expand_readahead(struct netfs_io_request *rreq)
{
unsigned int rsize = rreq->rsize;
loff_t misalignment, i_size = i_size_read(rreq->inode);
if (rsize < PAGE_SIZE)
return;
if (rsize < INT_MAX)
rsize = roundup_pow_of_two(rsize);
else
rsize = ((unsigned int)INT_MAX + 1) / 2;
misalignment = rreq->start & (rsize - 1);
if (misalignment) {
rreq->start -= misalignment;
rreq->len += misalignment;
}
rreq->len = round_up(rreq->len, rsize);
if (rreq->start < i_size && rreq->len > i_size - rreq->start)
rreq->len = i_size - rreq->start;
}
/*
* Completion of a request operation.
*/
@ -329,7 +300,6 @@ const struct netfs_request_ops cifs_req_ops = {
.init_request = cifs_init_request,
.free_request = cifs_free_request,
.free_subrequest = cifs_free_subrequest,
.expand_readahead = cifs_expand_readahead,
.clamp_length = cifs_clamp_length,
.issue_read = cifs_req_issue_read,
.done = cifs_rreq_done,