[PATCH] Shrinks sizeof(files_struct) and better layout
1) Reduce the size of (struct fdtable) to exactly 64 bytes on 32bits
platforms, lowering kmalloc() allocated space by 50%.
2) Reduce the size of (files_struct), using a special 32 bits (or
64bits) embedded_fd_set, instead of a 1024 bits fd_set for the
close_on_exec_init and open_fds_init fields. This save some ram (248
bytes per task) as most tasks dont open more than 32 files. D-Cache
footprint for such tasks is also reduced to the minimum.
3) Reduce size of allocated fdset. Currently two full pages are
allocated, that is 32768 bits on x86 for example, and way too much. The
minimum is now L1_CACHE_BYTES.
UP and SMP should benefit from this patch, because most tasks will touch
only one cache line when open()/close() stdin/stdout/stderr (0/1/2),
(next_fd, close_on_exec_init, open_fds_init, fd_array[0 .. 2] being in the
same cache line)
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/open.c b/fs/open.c
index 70e0230..1091dad 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -973,7 +973,7 @@
fdt = files_fdtable(files);
fd = find_next_zero_bit(fdt->open_fds->fds_bits,
fdt->max_fdset,
- fdt->next_fd);
+ files->next_fd);
/*
* N.B. For clone tasks sharing a files structure, this test
@@ -998,7 +998,7 @@
FD_SET(fd, fdt->open_fds);
FD_CLR(fd, fdt->close_on_exec);
- fdt->next_fd = fd + 1;
+ files->next_fd = fd + 1;
#if 1
/* Sanity check */
if (fdt->fd[fd] != NULL) {
@@ -1019,8 +1019,8 @@
{
struct fdtable *fdt = files_fdtable(files);
__FD_CLR(fd, fdt->open_fds);
- if (fd < fdt->next_fd)
- fdt->next_fd = fd;
+ if (fd < files->next_fd)
+ files->next_fd = fd;
}
void fastcall put_unused_fd(unsigned int fd)