On Wed, 9 Mar 2011 11:00:20 +0100
Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> On Wed, Mar 09, 2011 at 04:48:01PM +0900, KAMEZAWA Hiroyuki wrote:
> > On Wed, 9 Mar 2011 15:07:50 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> >
> > > > } else {
> > > > /* shmem */
> > > > if (PageSwapCache(page)) {
> > > > ..
> > > > } else {
> > > > ..
> > > > }
> > > > }
> > > >
> > > > Otherwise, the page cache will be charged twice.
> > > >
> > >
> > > Ahh, thanks. I'll send v3.
> > >
> >
> > Okay, this is a fixed one.
> > ==
> >
> > fs/fuse/dev.c::fuse_try_move_page() does
> >
> > (1) remove a page by ->steal()
> > (2) re-add the page to page cache
> > (3) link the page to LRU if it was not on LRU at (1)
> >
> > This implies the page is _on_ LRU when it's added to radix-tree.
> > So, the page is added to memory cgroup while it's on LRU.
> > because LRU is lazy and no one flushs it.
> >
> > This is the same behavior as SwapCache and needs special care as
> > - remove page from LRU before overwrite pc->mem_cgroup.
> > - add page to LRU after overwrite pc->mem_cgroup.
> >
> > And we need to taking care of pagevec.
> >
> > If PageLRU(page) is set before we add PCG_USED bit, the page
> > will not be added to memcg's LRU (in short period).
> > So, regardlress of PageLRU(page) value before commit_charge(),
> > we need to check PageLRU(page) after commit_charge().
> >
> > Changelog v2=>v3:
> > - fixed double accounting.
> >
> > Changelog v1=>v2:
> > - clean up.
> > - cover !PageLRU() by pagevec case.
> >
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> Thanks for the fix. I have a few comments below. Only nitpicks
> though, the patch looks correct to me.
>
> Reviewed-by: Johannes Weiner <hannes@xxxxxxxxxxx>
>
Thank you for review.
> > @@ -2431,9 +2430,28 @@ static void
> > __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
> > enum charge_type ctype);
> >
> > +static void
> > +__mem_cgroup_commit_charge_lrucare(struct page *page, struct mem_cgroup *mem,
> > + enum charge_type ctype)
> > +{
> > + struct page_cgroup *pc = lookup_page_cgroup(page);
> > + /*
> > + * In some case, SwapCache, FUSE(splice_buf->radixtree), the page
> > + * is already on LRU. It means the page may on some other page_cgroup's
> > + * LRU. Take care of it.
> > + */
> > + if (unlikely(PageLRU(page)))
> > + mem_cgroup_lru_del_before_commit(page);
>
> Do we need the extra check? mem_cgroup_lru_del_before_commit() will
> do the right thing if the page is not on the list.
>
lru_del_before_commit does checks under zone->lru_lock. So, it's very very heavy.
Hmm, I'll move the check under mem_cgroup_lru_del_before_commit() before lock.
> > + __mem_cgroup_commit_charge(mem, page, 1, pc, ctype);
> > + if (unlikely(PageLRU(page)))
> > + mem_cgroup_lru_add_after_commit(page);
>
> Same here, mem_cgroup_lru_add_after_commit() has its own check for
> PG_lru.
>
I'll move the check.
> > @@ -2468,14 +2486,16 @@ int mem_cgroup_cache_charge(struct page
> > if (unlikely(!mm))
> > mm = &init_mm;
> >
> > - if (page_is_file_cache(page))
> > - return mem_cgroup_charge_common(page, mm, gfp_mask,
> > - MEM_CGROUP_CHARGE_TYPE_CACHE);
> > -
> > + if (page_is_file_cache(page)) {
> > + ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, &mem, true);
> > + if (ret || !mem)
> > + return ret;
> > + __mem_cgroup_commit_charge_lrucare(page, mem,
> > + MEM_CGROUP_CHARGE_TYPE_CACHE);
>
> I think the comment about why we need to take care of the LRU status
> would make more sense here (rather than in the _lrucare function),
> because it is here where you make handling the lru a consequence of
> the page being a file page.
>
Sure.
> How about this?
>
> /*
> * FUSE reuses pages without going through the final
> * put that would remove them from the LRU list, make
> * sure that they get relinked properly.
> */
will add. Thank you !
-Kame
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