From 997778e332e9f6d3d1c42e9a222fcab8d4732c40 Mon Sep 17 00:00:00 2001

From: Michal Sekletar <msekleta@redhat.com>

Date: Fri, 27 May 2016 14:29:17 +0200

Subject: [PATCH] readahead: do not increase nr_requests for root fs block

 device

Having nr_requests can cause system lockups. Arguably, this should get

fixed somehow in kernel. For now we just stop changing the

value.

Note that not bumping a value may cause that posix_fadvise call

will block in case there is no room in a request queue.

See: http://article.gmane.org/gmane.linux.kernel/1072356

RHEL-only

Resolves: #1314559

---

 src/readahead/readahead-common.c | 64 ----------------------------------------

 src/readahead/readahead-common.h |  2 --

 src/readahead/readahead-replay.c |  2 --

 3 files changed, 68 deletions(-)

diff --git a/src/readahead/readahead-common.c b/src/readahead/readahead-common.c

index 3ca48a7..6cf33f7 100644

--- a/src/readahead/readahead-common.c

+++ b/src/readahead/readahead-common.c

@@ -253,70 +253,6 @@ ReadaheadShared *shared_get(void) {

         return m;

 }

-/* We use 20K instead of the more human digestable 16K here. Why?

-   Simply so that it is more unlikely that users end up picking this

-   value too so that we can recognize better whether the user changed

-   the value while we had it temporarily bumped. */

-#define BUMP_REQUEST_NR (20*1024u)

-

-int block_bump_request_nr(const char *p) {

-        struct stat st;

-        uint64_t u;

-        char *ap = NULL, *line = NULL;

-        int r;

-        dev_t d;

-

-        assert(p);

-

-        if (stat(p, &st) < 0)

-                return -errno;

-

-        if (major(st.st_dev) == 0)

-                return 0;

-

-        d = st.st_dev;

-        block_get_whole_disk(d, &d);

-

-        if (asprintf(&ap, "/sys/dev/block/%u:%u/queue/nr_requests", major(d), minor(d)) < 0) {

-                r= -ENOMEM;

-                goto finish;

-        }

-

-        r = read_one_line_file(ap, &line);

-        if (r < 0) {

-                if (r == -ENOENT)

-                        r = 0;

-                goto finish;

-        }

-

-        r = safe_atou64(line, &u);

-        if (r >= 0 && u >= BUMP_REQUEST_NR) {

-                r = 0;

-                goto finish;

-        }

-

-        free(line);

-        line = NULL;

-

-        if (asprintf(&line, "%u", BUMP_REQUEST_NR) < 0) {

-                r = -ENOMEM;

-                goto finish;

-        }

-

-        r = write_string_file(ap, line);

-        if (r < 0)

-                goto finish;

-

-        log_info("Bumped block_nr parameter of %u:%u to %u. This is a temporary hack and should be removed one day.", major(d), minor(d), BUMP_REQUEST_NR);

-        r = 1;

-

-finish:

-        free(ap);

-        free(line);

-

-        return r;

-}

-

 int block_get_readahead(const char *p, uint64_t *bytes) {

         struct stat st;

         char *ap = NULL, *line = NULL;

diff --git a/src/readahead/readahead-common.h b/src/readahead/readahead-common.h

index b34f3aa..cc2ea81 100644

--- a/src/readahead/readahead-common.h

+++ b/src/readahead/readahead-common.h

@@ -51,8 +51,6 @@ typedef struct ReadaheadShared {

 ReadaheadShared *shared_get(void);

-int block_bump_request_nr(const char *p);

-

 int block_get_readahead(const char *p, uint64_t *bytes);

 int block_set_readahead(const char *p, uint64_t bytes);

diff --git a/src/readahead/readahead-replay.c b/src/readahead/readahead-replay.c

index f81e0fe..c2e2816 100644

--- a/src/readahead/readahead-replay.c

+++ b/src/readahead/readahead-replay.c

@@ -134,8 +134,6 @@ static int replay(const char *root) {

         assert(root);

-        block_bump_request_nr(root);

-

         if (asprintf(&pack_fn, "%s/.readahead", root) < 0)

                 return log_oom();