Chris Li <chrisl@xxxxxxxxxx> writes: > On Fri, Mar 10, 2023 at 11:06:37AM +0800, Huang, Ying wrote: >> > Unfortunately it's a little bit more. 24 is the extra overhead. >> > >> > Today we have an xarray entry for each swapped out page, that either >> > has the swapcache pointer or the shadow entry. >> > >> > With this implementation, we have an xarray entry for each swapped out >> > page, that has a pointer to the swap_desc. >> > >> > Ignoring the overhead of the xarray itself, we have (8 + 24) / (8 + 1) = 3.5556. >> >> OK. I see. We can only hold 8 bytes for each xarray entry. To save >> memory usage, we can allocate multiple swap_desc (e.g., 16) for each >> xarray entry. Then the memory usage of xarray becomes 1/N. > > The xarray look up key is the swap offset from the swap entry. If you > put more than one swap_desc under the one xarray entry. It will mean > all those different swap_descs will share a swap offset. For example, if we allocate 16 swap_desc for each xarray entry. Then, we can use (swap_desc_index >> 4) as key to lookup xarray, and (swap_desc_index & 0x15) to index inside 16 swap_desc for the xarray entry. Best Regards, Huang, Ying
