[dpdk-dev] [PATCH] mem: close rtemap files

[dpdk-dev] [PATCH] mem: close rtemap files

[Stephen Hemminger]

The memory subsystem is leaving open a file descriptor for each
rtemap file. This can lead to hundreds of extra open file descriptors
which has negative side effects. For example, the application may go
over its maximum file descriptor limit, or the application may be using
limited API's like select that only allow 1024 file descriptors.

The EAL memory subsystem does not need to hold the file open.
Probably the original intention was to keep the file locked, but that is
not necessary. The Linux kernel keeps a reference count on the file,
and the mmap counts is a reference and therefore maintains the file
as locked.

The fix is one line just close the file after it is setup.

Fixes: 582bed1e1d1d ("mem: support mapping hugepages at runtime")
Cc: anatoly.burakov@intel.com
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/librte_eal/linux/eal_memalloc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/librte_eal/linux/eal_memalloc.c b/lib/librte_eal/linux/eal_memalloc.c
index 6dc1b2baecdc..99600adda568 100644
--- a/lib/librte_eal/linux/eal_memalloc.c
+++ b/lib/librte_eal/linux/eal_memalloc.c
@@ -651,6 +651,12 @@ alloc_seg(struct rte_memseg *ms, void *addr, int socket_id,
 				__func__);
 #endif
 
+	/*
+	 * reference count is held by mmap() now
+	 * don't need to hold file open to keep it locked
+	 */
+	close(fd);
+
 	ms->addr = addr;
 	ms->hugepage_sz = alloc_sz;
 	ms->len = alloc_sz;
-- 
2.27.0

Re: [dpdk-dev] [PATCH] mem: close rtemap files

[Stephen Hemminger]

On Mon, 19 Oct 2020 08:42:35 -0700
Stephen Hemminger <stephen@networkplumber.org> wrote:

> The memory subsystem is leaving open a file descriptor for each
> rtemap file. This can lead to hundreds of extra open file descriptors
> which has negative side effects. For example, the application may go
> over its maximum file descriptor limit, or the application may be using
> limited API's like select that only allow 1024 file descriptors.
> 
> The EAL memory subsystem does not need to hold the file open.
> Probably the original intention was to keep the file locked, but that is
> not necessary. The Linux kernel keeps a reference count on the file,
> and the mmap counts is a reference and therefore maintains the file
> as locked.
> 
> The fix is one line just close the file after it is setup.
> 
> Fixes: 582bed1e1d1d ("mem: support mapping hugepages at runtime")
> Cc: anatoly.burakov@intel.com
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

This is fixes the open files, but has issues on shutdown.
Will send new version later.