Re: [PATCH] mem: close rtemap files

[Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>]

2022-10-06 10:04 (UTC+0000), huzaifa.rahman:
> Bugzilla ID: 560
> 
> 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 just to close the file after it is setup.
> 
> Signed-off-by: huzaifa.rahman <huzaifa.rahman@emumba.com>
> ---
>  lib/eal/linux/eal_memalloc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/lib/eal/linux/eal_memalloc.c b/lib/eal/linux/eal_memalloc.c
> index f8b1588cae..955c4e4f95 100644
> --- a/lib/eal/linux/eal_memalloc.c
> +++ b/lib/eal/linux/eal_memalloc.c
> @@ -679,6 +679,9 @@ alloc_seg(struct rte_memseg *ms, void *addr, int socket_id,
>  
>  	huge_recover_sigbus();
>  
> +	close(fd);
> +	fd_list[list_idx].fds[seg_idx] = -1;
> +
>  	ms->addr = addr;
>  	ms->hugepage_sz = alloc_sz;
>  	ms->len = alloc_sz;

This breaks rte_memseg_get_fd().
If memfd_create() was used to open the file descriptor,
there seems no way to reopen it once closed.

--single-file-segments may be used to save FD count,
does using it solve your issue?