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When growing the file descriptor table, new larger memory chunk is

allocated, but the old table is kept around to handle the case of
threads still performing unlocked accesses to it.

Grow the table exponentially instead of increasing its size by
sizeof(long) * 8 chunks when overflowing. This mode significantly
reduces the total memory use for the processes consuming large numbers
of the file descriptors which open them one by one.

Reported and tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Approved by:	re (marius)
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1 parent 9375280 commit 7ff487b3a2f97b08f82ffdc0b157adf5e886b4f7 @kostikbel kostikbel committed Oct 9, 2013
Showing with 21 additions and 2 deletions.
  1. +21 −2 sys/kern/kern_descrip.c
@@ -119,6 +119,7 @@ static int closefp(struct filedesc *fdp, int fd, struct file *fp,
static int fd_first_free(struct filedesc *fdp, int low, int size);
static int fd_last_used(struct filedesc *fdp, int size);
static void fdgrowtable(struct filedesc *fdp, int nfd);
+static void fdgrowtable_exp(struct filedesc *fdp, int nfd);
static void fdunused(struct filedesc *fdp, int fd);
static void fdused(struct filedesc *fdp, int fd);
static int fill_pipe_info(struct pipe *pi, struct kinfo_file *kif);
@@ -855,7 +856,7 @@ do_dup(struct thread *td, int flags, int old, int new,
return (EMFILE);
}
#endif
- fdgrowtable(fdp, new + 1);
+ fdgrowtable_exp(fdp, new + 1);
oldfde = &fdp->fd_ofiles[old];
}
newfde = &fdp->fd_ofiles[new];
@@ -1478,6 +1479,24 @@ filecaps_validate(const struct filecaps *fcaps, const char *func)
("%s: ioctls without CAP_IOCTL", func));
}
+static void
+fdgrowtable_exp(struct filedesc *fdp, int nfd)
+{
+ int nfd1, maxfd;
+
+ FILEDESC_XLOCK_ASSERT(fdp);
+
+ nfd1 = fdp->fd_nfiles * 2;
+ if (nfd1 < nfd)
+ nfd1 = nfd;
+ maxfd = getmaxfd(curproc);
+ if (maxfd < nfd1)
+ nfd1 = maxfd;
+ KASSERT(nfd <= nfd1,
+ ("too low nfd1 %d %d %d %d", nfd, fdp->fd_nfiles, maxfd, nfd1));
+ fdgrowtable(fdp, nfd1);
+}
+
/*
* Grow the file table to accomodate (at least) nfd descriptors.
*/
@@ -1596,7 +1615,7 @@ fdalloc(struct thread *td, int minfd, int *result)
* fd is already equal to first free descriptor >= minfd, so
* we only need to grow the table and we are done.
*/
- fdgrowtable(fdp, allocfd);
+ fdgrowtable_exp(fdp, allocfd);
}
/*

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