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CIFS: Add asynchronous read support through kernel AIO
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This patch adds support to process read calls passed by io_submit()
asynchronously. It based on the previously introduced async context
that allows to process i/o responses in a separate thread and
return the caller immediately for asynchronous calls.

This improves reading performance of single threaded applications
with increasing of i/o queue depth size.

Signed-off-by: Pavel Shilovsky <[email protected]>
Signed-off-by: Steve French <[email protected]>
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@piastry @smfrench
piastry authored and smfrench committed May 2, 2017
1 parent ccf7f40 commit 6685c5e
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Showing 2 changed files with 131 additions and 39 deletions.
1 change: 1 addition & 0 deletions fs/cifs/cifsglob.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1140,6 +1140,7 @@ struct cifs_readdata {
struct completion done;
struct cifsFileInfo *cfile;
struct address_space *mapping;
struct cifs_aio_ctx *ctx;
__u64 offset;
unsigned int bytes;
unsigned int got_bytes;
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169 changes: 130 additions & 39 deletions fs/cifs/file.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2859,6 +2859,7 @@ cifs_uncached_readdata_release(struct kref *refcount)
struct cifs_readdata, refcount);
unsigned int i;

kref_put(&rdata->ctx->refcount, cifs_aio_ctx_release);
for (i = 0; i < rdata->nr_pages; i++) {
put_page(rdata->pages[i]);
rdata->pages[i] = NULL;
Expand Down Expand Up @@ -2900,13 +2901,17 @@ cifs_readdata_to_iov(struct cifs_readdata *rdata, struct iov_iter *iter)
return remaining ? -EFAULT : 0;
}

static void collect_uncached_read_data(struct cifs_aio_ctx *ctx);

static void
cifs_uncached_readv_complete(struct work_struct *work)
{
struct cifs_readdata *rdata = container_of(work,
struct cifs_readdata, work);

complete(&rdata->done);
collect_uncached_read_data(rdata->ctx);
/* the below call can possibly free the last ref to aio ctx */
kref_put(&rdata->refcount, cifs_uncached_readdata_release);
}

Expand Down Expand Up @@ -2973,7 +2978,8 @@ cifs_uncached_copy_into_pages(struct TCP_Server_Info *server,

static int
cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
struct cifs_sb_info *cifs_sb, struct list_head *rdata_list)
struct cifs_sb_info *cifs_sb, struct list_head *rdata_list,
struct cifs_aio_ctx *ctx)
{
struct cifs_readdata *rdata;
unsigned int npages, rsize, credits;
Expand Down Expand Up @@ -3020,6 +3026,8 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
rdata->read_into_pages = cifs_uncached_read_into_pages;
rdata->copy_into_pages = cifs_uncached_copy_into_pages;
rdata->credits = credits;
rdata->ctx = ctx;
kref_get(&ctx->refcount);

if (!rdata->cfile->invalidHandle ||
!(rc = cifs_reopen_file(rdata->cfile, true)))
Expand All @@ -3042,50 +3050,37 @@ cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
return rc;
}

ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
static void
collect_uncached_read_data(struct cifs_aio_ctx *ctx)
{
struct file *file = iocb->ki_filp;
ssize_t rc;
size_t len;
ssize_t total_read = 0;
loff_t offset = iocb->ki_pos;
struct cifs_readdata *rdata, *tmp;
struct iov_iter *to = &ctx->iter;
struct cifs_sb_info *cifs_sb;
struct cifs_tcon *tcon;
struct cifsFileInfo *open_file;
struct cifs_readdata *rdata, *tmp;
struct list_head rdata_list;

len = iov_iter_count(to);
if (!len)
return 0;
unsigned int i;
int rc;

INIT_LIST_HEAD(&rdata_list);
cifs_sb = CIFS_FILE_SB(file);
open_file = file->private_data;
tcon = tlink_tcon(open_file->tlink);
tcon = tlink_tcon(ctx->cfile->tlink);
cifs_sb = CIFS_SB(ctx->cfile->dentry->d_sb);

if (!tcon->ses->server->ops->async_readv)
return -ENOSYS;
mutex_lock(&ctx->aio_mutex);

if ((file->f_flags & O_ACCMODE) == O_WRONLY)
cifs_dbg(FYI, "attempting read on write only file instance\n");

rc = cifs_send_async_read(offset, len, open_file, cifs_sb, &rdata_list);

/* if at least one read request send succeeded, then reset rc */
if (!list_empty(&rdata_list))
rc = 0;
if (list_empty(&ctx->list)) {
mutex_unlock(&ctx->aio_mutex);
return;
}

len = iov_iter_count(to);
rc = ctx->rc;
/* the loop below should proceed in the order of increasing offsets */
again:
list_for_each_entry_safe(rdata, tmp, &rdata_list, list) {
list_for_each_entry_safe(rdata, tmp, &ctx->list, list) {
if (!rc) {
/* FIXME: freezable sleep too? */
rc = wait_for_completion_killable(&rdata->done);
if (rc)
rc = -EINTR;
else if (rdata->result == -EAGAIN) {
if (!try_wait_for_completion(&rdata->done)) {
mutex_unlock(&ctx->aio_mutex);
return;
}

if (rdata->result == -EAGAIN) {
/* resend call if it's a retryable error */
struct list_head tmp_list;
unsigned int got_bytes = rdata->got_bytes;
Expand All @@ -3111,9 +3106,9 @@ ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
rdata->offset + got_bytes,
rdata->bytes - got_bytes,
rdata->cfile, cifs_sb,
&tmp_list);
&tmp_list, ctx);

list_splice(&tmp_list, &rdata_list);
list_splice(&tmp_list, &ctx->list);

kref_put(&rdata->refcount,
cifs_uncached_readdata_release);
Expand All @@ -3131,14 +3126,110 @@ ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
kref_put(&rdata->refcount, cifs_uncached_readdata_release);
}

total_read = len - iov_iter_count(to);
for (i = 0; i < ctx->npages; i++) {
if (ctx->should_dirty)
set_page_dirty(ctx->bv[i].bv_page);
put_page(ctx->bv[i].bv_page);
}

cifs_stats_bytes_read(tcon, total_read);
ctx->total_len = ctx->len - iov_iter_count(to);

cifs_stats_bytes_read(tcon, ctx->total_len);

/* mask nodata case */
if (rc == -ENODATA)
rc = 0;

ctx->rc = (rc == 0) ? ctx->total_len : rc;

mutex_unlock(&ctx->aio_mutex);

if (ctx->iocb && ctx->iocb->ki_complete)
ctx->iocb->ki_complete(ctx->iocb, ctx->rc, 0);
else
complete(&ctx->done);
}

ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
{
struct file *file = iocb->ki_filp;
ssize_t rc;
size_t len;
ssize_t total_read = 0;
loff_t offset = iocb->ki_pos;
struct cifs_sb_info *cifs_sb;
struct cifs_tcon *tcon;
struct cifsFileInfo *cfile;
struct cifs_aio_ctx *ctx;

len = iov_iter_count(to);
if (!len)
return 0;

cifs_sb = CIFS_FILE_SB(file);
cfile = file->private_data;
tcon = tlink_tcon(cfile->tlink);

if (!tcon->ses->server->ops->async_readv)
return -ENOSYS;

if ((file->f_flags & O_ACCMODE) == O_WRONLY)
cifs_dbg(FYI, "attempting read on write only file instance\n");

ctx = cifs_aio_ctx_alloc();
if (!ctx)
return -ENOMEM;

ctx->cfile = cifsFileInfo_get(cfile);

if (!is_sync_kiocb(iocb))
ctx->iocb = iocb;

if (to->type & ITER_IOVEC)
ctx->should_dirty = true;

rc = setup_aio_ctx_iter(ctx, to, READ);
if (rc) {
kref_put(&ctx->refcount, cifs_aio_ctx_release);
return rc;
}

len = ctx->len;

/* grab a lock here due to read response handlers can access ctx */
mutex_lock(&ctx->aio_mutex);

rc = cifs_send_async_read(offset, len, cfile, cifs_sb, &ctx->list, ctx);

/* if at least one read request send succeeded, then reset rc */
if (!list_empty(&ctx->list))
rc = 0;

mutex_unlock(&ctx->aio_mutex);

if (rc) {
kref_put(&ctx->refcount, cifs_aio_ctx_release);
return rc;
}

if (!is_sync_kiocb(iocb)) {
kref_put(&ctx->refcount, cifs_aio_ctx_release);
return -EIOCBQUEUED;
}

rc = wait_for_completion_killable(&ctx->done);
if (rc) {
mutex_lock(&ctx->aio_mutex);
ctx->rc = rc = -EINTR;
total_read = ctx->total_len;
mutex_unlock(&ctx->aio_mutex);
} else {
rc = ctx->rc;
total_read = ctx->total_len;
}

kref_put(&ctx->refcount, cifs_aio_ctx_release);

if (total_read) {
iocb->ki_pos += total_read;
return total_read;
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