Re: [mmtom] please drop memcg-handle-swap-cache set (memcg handle swap cache rework).

[Balbir Singh <balbir@linux.vnet.ibm.com>]

KAMEZAWA Hiroyuki wrote:
> Now, SwapCache is handled by memcg (in -mm) but it became complicated than I thought of.
> 
> followings are queued in -mm now.
>   memcg-handle-swap-cache.patch
>   memcg-handle-swap-cache-fix.patch
>   memcg-handle-swap-cache-fix-shmem-page-migration-incorrectness-on-memcgroup.patch
> 
> And I have memcg-handle-shmem-swap-cache-fix.patch....
> 
> Balbir argued that "This is too complicated!", ok, let's rework.
> 

Thanks, it was complicated and simplification is always welcome!

> Andrew, could you drop above 3 patches ? I'd like to retry with clear logic.
> 
> I'm testing this new version now. Basic logic is not changed but corner case
> handling is clearer than previous one. If there is something unclear, 
> please tell me.  I'd like to write easy-to-understand one.
> 
> ==
> This patch tries to catch SwapCache usage by memcg in following Rule.
> 
> 1. just ignore add_to_swap_cache()
> 2. if a page is uncharged,
> 	(a) don't uncharge when PageSwapCache(page)
> 	(b) don't uncharge when the page is mapped.
> 	(c) don't uncharge when the page is still on radix-tree.
>             This can be checked by (page->mapping && !PageAnon(page))
> 
> 3. __delete_from_swap_cache() calles uncharge after clearing PageSwapCache flag.
> 4. mem_cgroup_uncharge_cache() is called only after page->mapping is cleared.
> 5. migration has some corner case and handled.
> 

My understanding of this patchset now is that

If the page was ever mapped or cached, we don't tweak add_to_swap_cache(),
instead, we keep the page around in the memcg, till it is removed from swap
cache. Is my understanding of your intent correct?

[snip]

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL

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