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[nginx] Simplified sendfile(SF_NODISKIO) usage.

Maxim Dounin
December 27, 2021 01:50PM
details: https://hg.nginx.org/nginx/rev/ec2e6893caaa
branches:
changeset: 7985:ec2e6893caaa
user: Maxim Dounin <mdounin@mdounin.ru>
date: Mon Dec 27 19:48:33 2021 +0300
description:
Simplified sendfile(SF_NODISKIO) usage.

Starting with FreeBSD 11, there is no need to use AIO operations to preload
data into cache for sendfile(SF_NODISKIO) to work. Instead, sendfile()
handles non-blocking loading data from disk by itself. It still can, however,
return EBUSY if a page is already being loaded (for example, by a different
process). If this happens, we now post an event for the next event loop
iteration, so sendfile() is retried "after a short period", as manpage
recommends.

The limit of the number of EBUSY tolerated without any progress is preserved,
but now it does not result in an alert, since on an idle system event loop
iteration might be very short and EBUSY can happen many times in a row.
Instead, SF_NODISKIO is simply disabled for one call once the limit is
reached.

With this change, sendfile(SF_NODISKIO) is now used automatically as long as
sendfile() is enabled, and no longer requires "aio on;".

diffstat:

auto/os/freebsd | 8 +-
src/core/ngx_buf.h | 3 -
src/core/ngx_connection.h | 2 +-
src/core/ngx_module.h | 2 +-
src/core/ngx_output_chain.c | 32 ------------
src/event/ngx_event.h | 4 -
src/http/ngx_http_copy_filter_module.c | 82 --------------------------------
src/os/unix/ngx_freebsd_sendfile_chain.c | 74 ++++++++++-----------------
8 files changed, 33 insertions(+), 174 deletions(-)

diffs (367 lines):

diff -r ae992b5a27b2 -r ec2e6893caaa auto/os/freebsd
--- a/auto/os/freebsd Mon Dec 27 19:47:05 2021 +0300
+++ b/auto/os/freebsd Mon Dec 27 19:48:33 2021 +0300
@@ -44,12 +44,10 @@ if [ $osreldate -gt 300007 ]; then
CORE_SRCS="$CORE_SRCS $FREEBSD_SENDFILE_SRCS"
fi

-if [ $NGX_FILE_AIO = YES ]; then
- if [ $osreldate -gt 502103 ]; then
- echo " + sendfile()'s SF_NODISKIO found"
+if [ $osreldate -gt 1100093 ]; then
+ echo " + sendfile()'s SF_NODISKIO found"

- have=NGX_HAVE_AIO_SENDFILE . auto/have
- fi
+ have=NGX_HAVE_SENDFILE_NODISKIO . auto/have
fi

# POSIX semaphores
diff -r ae992b5a27b2 -r ec2e6893caaa src/core/ngx_buf.h
--- a/src/core/ngx_buf.h Mon Dec 27 19:47:05 2021 +0300
+++ b/src/core/ngx_buf.h Mon Dec 27 19:48:33 2021 +0300
@@ -90,9 +90,6 @@ struct ngx_output_chain_ctx_s {

#if (NGX_HAVE_FILE_AIO || NGX_COMPAT)
ngx_output_chain_aio_pt aio_handler;
-#if (NGX_HAVE_AIO_SENDFILE || NGX_COMPAT)
- ssize_t (*aio_preload)(ngx_buf_t *file);
-#endif
#endif

#if (NGX_THREADS || NGX_COMPAT)
diff -r ae992b5a27b2 -r ec2e6893caaa src/core/ngx_connection.h
--- a/src/core/ngx_connection.h Mon Dec 27 19:47:05 2021 +0300
+++ b/src/core/ngx_connection.h Mon Dec 27 19:48:33 2021 +0300
@@ -185,7 +185,7 @@ struct ngx_connection_s {

unsigned need_last_buf:1;

-#if (NGX_HAVE_AIO_SENDFILE || NGX_COMPAT)
+#if (NGX_HAVE_SENDFILE_NODISKIO || NGX_COMPAT)
unsigned busy_count:2;
#endif

diff -r ae992b5a27b2 -r ec2e6893caaa src/core/ngx_module.h
--- a/src/core/ngx_module.h Mon Dec 27 19:47:05 2021 +0300
+++ b/src/core/ngx_module.h Mon Dec 27 19:48:33 2021 +0300
@@ -41,7 +41,7 @@
#define NGX_MODULE_SIGNATURE_3 "0"
#endif

-#if (NGX_HAVE_AIO_SENDFILE || NGX_COMPAT)
+#if (NGX_HAVE_SENDFILE_NODISKIO || NGX_COMPAT)
#define NGX_MODULE_SIGNATURE_4 "1"
#else
#define NGX_MODULE_SIGNATURE_4 "0"
diff -r ae992b5a27b2 -r ec2e6893caaa src/core/ngx_output_chain.c
--- a/src/core/ngx_output_chain.c Mon Dec 27 19:47:05 2021 +0300
+++ b/src/core/ngx_output_chain.c Mon Dec 27 19:48:33 2021 +0300
@@ -29,10 +29,6 @@

static ngx_inline ngx_int_t
ngx_output_chain_as_is(ngx_output_chain_ctx_t *ctx, ngx_buf_t *buf);
-#if (NGX_HAVE_AIO_SENDFILE)
-static ngx_int_t ngx_output_chain_aio_setup(ngx_output_chain_ctx_t *ctx,
- ngx_file_t *file);
-#endif
static ngx_int_t ngx_output_chain_add_copy(ngx_pool_t *pool,
ngx_chain_t **chain, ngx_chain_t *in);
static ngx_int_t ngx_output_chain_align_file_buf(ngx_output_chain_ctx_t *ctx,
@@ -283,12 +279,6 @@ ngx_output_chain_as_is(ngx_output_chain_
buf->in_file = 0;
}

-#if (NGX_HAVE_AIO_SENDFILE)
- if (ctx->aio_preload && buf->in_file) {
- (void) ngx_output_chain_aio_setup(ctx, buf->file);
- }
-#endif
-
if (ctx->need_in_memory && !ngx_buf_in_memory(buf)) {
return 0;
}
@@ -301,28 +291,6 @@ ngx_output_chain_as_is(ngx_output_chain_
}


-#if (NGX_HAVE_AIO_SENDFILE)
-
-static ngx_int_t
-ngx_output_chain_aio_setup(ngx_output_chain_ctx_t *ctx, ngx_file_t *file)
-{
- ngx_event_aio_t *aio;
-
- if (file->aio == NULL && ngx_file_aio_init(file, ctx->pool) != NGX_OK) {
- return NGX_ERROR;
- }
-
- aio = file->aio;
-
- aio->data = ctx->filter_ctx;
- aio->preload_handler = ctx->aio_preload;
-
- return NGX_OK;
-}
-
-#endif
-
-
static ngx_int_t
ngx_output_chain_add_copy(ngx_pool_t *pool, ngx_chain_t **chain,
ngx_chain_t *in)
diff -r ae992b5a27b2 -r ec2e6893caaa src/event/ngx_event.h
--- a/src/event/ngx_event.h Mon Dec 27 19:47:05 2021 +0300
+++ b/src/event/ngx_event.h Mon Dec 27 19:48:33 2021 +0300
@@ -147,10 +147,6 @@ struct ngx_event_aio_s {

ngx_fd_t fd;

-#if (NGX_HAVE_AIO_SENDFILE || NGX_COMPAT)
- ssize_t (*preload_handler)(ngx_buf_t *file);
-#endif
-
#if (NGX_HAVE_EVENTFD)
int64_t res;
#endif
diff -r ae992b5a27b2 -r ec2e6893caaa src/http/ngx_http_copy_filter_module.c
--- a/src/http/ngx_http_copy_filter_module.c Mon Dec 27 19:47:05 2021 +0300
+++ b/src/http/ngx_http_copy_filter_module.c Mon Dec 27 19:48:33 2021 +0300
@@ -19,10 +19,6 @@ typedef struct {
static void ngx_http_copy_aio_handler(ngx_output_chain_ctx_t *ctx,
ngx_file_t *file);
static void ngx_http_copy_aio_event_handler(ngx_event_t *ev);
-#if (NGX_HAVE_AIO_SENDFILE)
-static ssize_t ngx_http_copy_aio_sendfile_preload(ngx_buf_t *file);
-static void ngx_http_copy_aio_sendfile_event_handler(ngx_event_t *ev);
-#endif
#endif
#if (NGX_THREADS)
static ngx_int_t ngx_http_copy_thread_handler(ngx_thread_task_t *task,
@@ -128,9 +124,6 @@ ngx_http_copy_filter(ngx_http_request_t
#if (NGX_HAVE_FILE_AIO)
if (ngx_file_aio && clcf->aio == NGX_HTTP_AIO_ON) {
ctx->aio_handler = ngx_http_copy_aio_handler;
-#if (NGX_HAVE_AIO_SENDFILE)
- ctx->aio_preload = ngx_http_copy_aio_sendfile_preload;
-#endif
}
#endif

@@ -207,81 +200,6 @@ ngx_http_copy_aio_event_handler(ngx_even
ngx_http_run_posted_requests(c);
}

-
-#if (NGX_HAVE_AIO_SENDFILE)
-
-static ssize_t
-ngx_http_copy_aio_sendfile_preload(ngx_buf_t *file)
-{
- ssize_t n;
- static u_char buf[1];
- ngx_event_aio_t *aio;
- ngx_http_request_t *r;
- ngx_output_chain_ctx_t *ctx;
-
- aio = file->file->aio;
- r = aio->data;
-
- if (r->aio) {
- /*
- * tolerate sendfile() calls if another operation is already
- * running; this can happen due to subrequests, multiple calls
- * of the next body filter from a filter, or in HTTP/2 due to
- * a write event on the main connection
- */
-
- return NGX_AGAIN;
- }
-
- n = ngx_file_aio_read(file->file, buf, 1, file->file_pos, NULL);
-
- if (n == NGX_AGAIN) {
- aio->handler = ngx_http_copy_aio_sendfile_event_handler;
-
- r->main->blocked++;
- r->aio = 1;
-
- ctx = ngx_http_get_module_ctx(r, ngx_http_copy_filter_module);
- ctx->aio = 1;
- }
-
- return n;
-}
-
-
-static void
-ngx_http_copy_aio_sendfile_event_handler(ngx_event_t *ev)
-{
- ngx_event_aio_t *aio;
- ngx_connection_t *c;
- ngx_http_request_t *r;
-
- aio = ev->data;
- r = aio->data;
- c = r->connection;
-
- r->main->blocked--;
- r->aio = 0;
- ev->complete = 0;
-
-#if (NGX_HTTP_V2)
-
- if (r->stream) {
- /*
- * for HTTP/2, update write event to make sure processing will
- * reach the main connection to handle sendfile() preload
- */
-
- c->write->ready = 1;
- c->write->active = 0;
- }
-
-#endif
-
- c->write->handler(c->write);
-}
-
-#endif
#endif


diff -r ae992b5a27b2 -r ec2e6893caaa src/os/unix/ngx_freebsd_sendfile_chain.c
--- a/src/os/unix/ngx_freebsd_sendfile_chain.c Mon Dec 27 19:47:05 2021 +0300
+++ b/src/os/unix/ngx_freebsd_sendfile_chain.c Mon Dec 27 19:48:33 2021 +0300
@@ -32,23 +32,22 @@
ngx_chain_t *
ngx_freebsd_sendfile_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
{
- int rc, flags;
- off_t send, prev_send, sent;
- size_t file_size;
- ssize_t n;
- ngx_uint_t eintr, eagain;
- ngx_err_t err;
- ngx_buf_t *file;
- ngx_event_t *wev;
- ngx_chain_t *cl;
- ngx_iovec_t header, trailer;
- struct sf_hdtr hdtr;
- struct iovec headers[NGX_IOVS_PREALLOCATE];
- struct iovec trailers[NGX_IOVS_PREALLOCATE];
-#if (NGX_HAVE_AIO_SENDFILE)
- ngx_uint_t ebusy;
- ngx_event_aio_t *aio;
+ int rc, flags;
+ off_t send, prev_send, sent;
+ size_t file_size;
+ ssize_t n;
+ ngx_err_t err;
+ ngx_buf_t *file;
+ ngx_uint_t eintr, eagain;
+#if (NGX_HAVE_SENDFILE_NODISKIO)
+ ngx_uint_t ebusy;
#endif
+ ngx_event_t *wev;
+ ngx_chain_t *cl;
+ ngx_iovec_t header, trailer;
+ struct sf_hdtr hdtr;
+ struct iovec headers[NGX_IOVS_PREALLOCATE];
+ struct iovec trailers[NGX_IOVS_PREALLOCATE];

wev = c->write;

@@ -77,11 +76,6 @@ ngx_freebsd_sendfile_chain(ngx_connectio
eagain = 0;
flags = 0;

-#if (NGX_HAVE_AIO_SENDFILE && NGX_SUPPRESS_WARN)
- aio = NULL;
- file = NULL;
-#endif
-
header.iovs = headers;
header.nalloc = NGX_IOVS_PREALLOCATE;

@@ -90,7 +84,7 @@ ngx_freebsd_sendfile_chain(ngx_connectio

for ( ;; ) {
eintr = 0;
-#if (NGX_HAVE_AIO_SENDFILE)
+#if (NGX_HAVE_SENDFILE_NODISKIO)
ebusy = 0;
#endif
prev_send = send;
@@ -179,9 +173,8 @@ ngx_freebsd_sendfile_chain(ngx_connectio

sent = 0;

-#if (NGX_HAVE_AIO_SENDFILE)
- aio = file->file->aio;
- flags = (aio && aio->preload_handler) ? SF_NODISKIO : 0;
+#if (NGX_HAVE_SENDFILE_NODISKIO)
+ flags = (c->busy_count <= 2) ? SF_NODISKIO : 0;
#endif

rc = sendfile(file->file->fd, c->fd, file->file_pos,
@@ -199,7 +192,7 @@ ngx_freebsd_sendfile_chain(ngx_connectio
eintr = 1;
break;

-#if (NGX_HAVE_AIO_SENDFILE)
+#if (NGX_HAVE_SENDFILE_NODISKIO)
case NGX_EBUSY:
ebusy = 1;
break;
@@ -252,41 +245,30 @@ ngx_freebsd_sendfile_chain(ngx_connectio

in = ngx_chain_update_sent(in, sent);

-#if (NGX_HAVE_AIO_SENDFILE)
+#if (NGX_HAVE_SENDFILE_NODISKIO)

if (ebusy) {
if (sent == 0) {
c->busy_count++;

- if (c->busy_count > 2) {
- ngx_log_error(NGX_LOG_ALERT, c->log, 0,
- "sendfile(%V) returned busy again",
- &file->file->name);
-
- c->busy_count = 0;
- aio->preload_handler = NULL;
-
- send = prev_send;
- continue;
- }
+ ngx_log_debug1(NGX_LOG_DEBUG_EVENT, c->log, 0,
+ "sendfile() busy, count:%d", c->busy_count);

} else {
c->busy_count = 0;
}

- n = aio->preload_handler(file);
-
- if (n > 0) {
- send = prev_send + sent;
- continue;
+ if (wev->posted) {
+ ngx_delete_posted_event(wev);
}

+ ngx_post_event(wev, &ngx_posted_next_events);
+
+ wev->ready = 0;
return in;
}

- if (flags == SF_NODISKIO) {
- c->busy_count = 0;
- }
+ c->busy_count = 0;

#endif

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[nginx] Simplified sendfile(SF_NODISKIO) usage.

Maxim Dounin 312 December 27, 2021 01:50PM



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