> What I recommend is below. (Please see the newest -mm because of a bug fix for
> mem cgroup) Considering page management on radix-tree, it can be considerd as
> a kind of page-migration, which replaces pages on radix-tree.
>
> ==
>
> > +int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
> > +{
> > + int error;
> > +
> > + VM_BUG_ON(!PageLocked(old));
> > + VM_BUG_ON(!PageLocked(new));
> > + VM_BUG_ON(new->mapping);
> > +
> struct mem_cgroup *memcg;
>
I think it should be initialized to NULL.
> error = mem_cgroup_prepare_migration(old, new, &memcg);
I want some comments like:
/*
* This is not page migration, but prepare_migration and end_migration
* does enough work for charge replacement.
*/
> #
> # This function will charge against "newpage". But this expects
> # the caller allows GFP_KERNEL gfp_mask.
> # After this, the newpage is in "charged" state.
> if (error)
> return -ENOMEM;
>
> > + error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
> > + if (!error) {
> > + struct address_space *mapping = old->mapping;
> > + pgoff_t offset = old->index;
> > +
> > + page_cache_get(new);
> > + new->mapping = mapping;
> > + new->index = offset;
> > +
> > + spin_lock_irq(&mapping->tree_lock);
> > + __remove_from_page_cache(old);
> > + error = radix_tree_insert(&mapping->page_tree, offset, new);
> > + BUG_ON(error);
> > + mapping->nrpages++;
> > + __inc_zone_page_state(new, NR_FILE_PAGES);
> > + if (PageSwapBacked(new))
> > + __inc_zone_page_state(new, NR_SHMEM);
> > + spin_unlock_irq(&mapping->tree_lock);
> > + radix_tree_preload_end();
>
> > + mem_cgroup_replace_cache_page(old, new); <== remove this.
>
> mem_cgroup_end_migraton(memcg, old, new, true);
>
> > + page_cache_release(old);
> > + }
> else
> mem_cgroup_end_migration(memcg, old, new, false);
>
> # Here, if the 4th argument is true, old page is uncharged.
> # if the 4th argument is false, the new page is uncharged.
> # Then, "charge" of the old page will be migrated onto the new page
> # if replacement is done.
>
>
>
> > +
> > + return error;
> > +}
> > +EXPORT_SYMBOL_GPL(replace_page_cache_page);
> > +
>
> ==
>
> I think this is enough simple and this covers all memory cgroup's racy
> problems.
>
I agree.
Thanks,
Daisuke Nishimura.
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