David Hildenbrand <david@xxxxxxxxxx> writes: > On 16.05.23 07:29, Huang Ying wrote: >> The general rule to use a swap entry is as follows. >> When we get a swap entry, if there isn't some other way to prevent >> swapoff, such as page lock for swap cache, page table lock, etc., the >> swap entry may become invalid because of swapoff. Then, we need to >> enclose all swap related functions with get_swap_device() and >> put_swap_device(), unless the swap functions call >> get/put_swap_device() by themselves. >> Add the rule as comments of get_swap_device(), and cleanup some >> functions which call get/put_swap_device(). >> 1. Enlarge the get/put_swap_device() protection range in >> __read_swap_cache_async(). This makes the function a little easier to >> be understood because we don't need to consider swapoff. And this >> makes it possible to remove get/put_swap_device() calling in some >> function called by __read_swap_cache_async(). >> 2. Remove get/put_swap_device() in __swap_count(). Which is call in >> do_swap_page() only, which encloses the call with get/put_swap_device() >> already. >> 3. Remove get/put_swap_device() in __swp_swapcount(). Which is call >> in __read_swap_cache_async() only, which encloses the call with >> get/put_swap_device() already. >> 4. Remove get/put_swap_device() in __swap_duplicate(). Which is >> called >> by >> - swap_shmem_alloc(): the swap cache is locked. >> - copy_nonpresent_pte() -> swap_duplicate() and try_to_unmap_one() >> -> >> swap_duplicate(): the page table lock is held. >> - __read_swap_cache_async() -> swapcache_prepare(): enclosed with >> get/put_swap_device() already. >> Other get/put_swap_device() usages are checked too. > > I suggest splitting this patch up into logical pieces as outlined here > by you already. OK. Will do that in the next version. Best Regards, Huang, Ying
