Re: [patch] NEW: arca-vm-21, swapout via shrink_mmap using PG_dirty

Andrea Arcangeli
1999-01-18T12:17:13Z

On 18 Jan 1999, Eric W. Biederman wrote:

> LT> and (b) as you noticed, it increases fragmentation.
>
> This is only because he didn't implement any kind of request queue. A
> fifo queue of pages to write would have keep performance up at current
> levels.

Infact I didn't wanted having to alloc more memory in order to free memory
(it's something I like to avoid). But the point is that I think that
swapping out from shrink_mmap() even if doing ordered I/O is not a win.
Try, benchmark and let me know your results, maybe I am wrong. And with a
FIFO also shrink_mmap() would change in order to do what swap_out() is
doing right now. And btw I think that the fifo could be approssimated to a
browse in the swap cache.

> LT> The reason PG_dirty should be a win for shared mappings is: (a) it gets
> LT> rid of the file write semaphore problem in a very clean way and
>
> Nope. Because we can still have some try to write to file X.
> That write needs memory, and we try to swapout a mapping of file X.
> Unless you believe it implies the write outs then must use a seperate process.

Agreed. I just pointed this out, but maybe I did not understood _where_ we
should do the write to disk to reclaim memory.

Andrea Arcangeli