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ksmbd: avoid zeroing the read buffer in smb2_read()

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smb2_read() allocates the read payload buffer with kvzalloc(), zeroing up
to max_read_size bytes (1MB or more with multichannel) on every read,
only to immediately overwrite the region with file data via kernel_read().

The zero-fill is pure overhead: ksmbd_vfs_read() returns the number of
bytes actually read ('nbytes'), and only those nbytes are ever consumed -
they are pinned into the response iov (ksmbd_iov_pin_rsp_read()), sent
over the RDMA channel (smb2_read_rdma_channel()), or copied by the
compression path (ksmbd_compress_response() uses iov_len == nbytes). The
ALIGN(length, 8) tail padding and any short-read remainder are never read
or transmitted, so they need not be initialized.

Use kvmalloc() instead to skip the redundant zeroing. This reduces CPU
and memory-bandwidth usage on large sequential reads.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
Namjae Jeon 2026-06-26 10:49:16 +09:00 committed by Steve French
parent 47f0b34f6b
commit 6b9a2e09d4
1 changed files with 1 additions and 1 deletions
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2
fs/smb/server/smb2pdu.c
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@ -7324,7 +7324,7 @@ int smb2_read(struct ksmbd_work *work)
ksmbd_debug(SMB, "filename %pD, offset %lld, len %zu\n",
fp->filp, offset, length);
aux_payload_buf = kvzalloc(ALIGN(length, 8), KSMBD_DEFAULT_GFP);
aux_payload_buf = kvmalloc(ALIGN(length, 8), KSMBD_DEFAULT_GFP);
if (!aux_payload_buf) {
err = -ENOMEM;
goto out;