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SubjectRe: [PATCH v2] fs: use kmalloc() to allocate fdmem if possible
On Mon,  3 May 2010 03:02:00 +0800
Changli Gao <xiaosuo@gmail.com> wrote:

> use kmalloc() to allocate fdmem if possible.
>
> vmalloc() is used as a fallback solution for fdmem allocation. A new helper
> function __free_fdtable() is introduced to reduce the lines of code.
>
> A potential bug, vfree() a memory allocated by kmalloc(), is fixed.
>

Seems a reasonable thing to do. It might also be reasonable to make
vmalloc() try kmalloc() first, but that's a separate exercise.

> ----
> fs/file.c | 55 ++++++++++++++++++++++---------------------------------
> 1 file changed, 22 insertions(+), 33 deletions(-)
> diff --git a/fs/file.c b/fs/file.c
> index 34bb7f7..9af31ae 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -39,28 +39,27 @@ int sysctl_nr_open_max = 1024 * 1024; /* raised later */
> */
> static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
>
> -static inline void * alloc_fdmem(unsigned int size)
> +static inline void *alloc_fdmem(unsigned int size)
> {
> - if (size <= PAGE_SIZE)
> - return kmalloc(size, GFP_KERNEL);
> - else
> - return vmalloc(size);
> + void *data;
> +
> + data = kmalloc(size, GFP_KERNEL);

This most definitely should have __GFP_NOWARN.

> + if (data != NULL)
> + return data;
> +
> + return vmalloc(size);
> }
>
> -static inline void free_fdarr(struct fdtable *fdt)
> +static inline void free_fdmem(void *ptr)
> {
> - if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *)))
> - kfree(fdt->fd);
> - else
> - vfree(fdt->fd);
> + is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr);
> }
>
> -static inline void free_fdset(struct fdtable *fdt)
> +static inline void __free_fdtable(struct fdtable *fdt)
> {
> - if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2))
> - kfree(fdt->open_fds);
> - else
> - vfree(fdt->open_fds);
> + free_fdmem(fdt->fd);
> + free_fdmem(fdt->open_fds);
> + kfree(fdt);
> }

And these should be uninlined - they're too large to be inlined.

My version of gcc seems to just uninline them anyway, but forcing them
to be inlined with __always_inline indeed causes 70-80 bytes more text,
and we figure that larger text generally causes a slower kernel due to
cache eviction effects.




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