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In our production > > > > environment we have observed that a lot of machines are spending a > > > > significant amount of memory as buffer_head and can not be left as > > > > system memory overhead. > > > > > > > > Charging buffer_head is not as simple as adding __GFP_ACCOUNT to the > > > > allocation. The buffer_heads can be allocated in a memcg different from > > > > the memcg of the page for which buffer_heads are being allocated. One > > > > concrete example is memory reclaim. The reclaim can trigger I/O of pages > > > > of any memcg on the system. So, the right way to charge buffer_head is > > > > to extract the memcg from the page for which buffer_heads are being > > > > allocated and then use targeted memcg charging API. > > > > > > > > Signed-off-by: Shakeel Butt > > > > Cc: Jan Kara > > > > Cc: Greg Thelen > > > > Cc: Michal Hocko > > > > Cc: Johannes Weiner > > > > Cc: Vladimir Davydov > > > > Cc: Alexander Viro > > > > Cc: Andrew Morton > > > > --- > > > > fs/buffer.c | 14 +++++++++++++- > > > > include/linux/memcontrol.h | 7 +++++++ > > > > mm/memcontrol.c | 21 +++++++++++++++++++++ > > > > 3 files changed, 41 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/fs/buffer.c b/fs/buffer.c > > > > index 8194e3049fc5..26389b7a3cab 100644 > > > > --- a/fs/buffer.c > > > > +++ b/fs/buffer.c > > > > @@ -815,10 +815,17 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size, > > > > struct buffer_head *bh, *head; > > > > gfp_t gfp = GFP_NOFS; > > > > long offset; > > > > + struct mem_cgroup *old_memcg; > > > > + struct mem_cgroup *memcg = get_mem_cgroup_from_page(page); > > > > > > > > if (retry) > > > > gfp |= __GFP_NOFAIL; > > > > > > > > + if (memcg) { > > > > + gfp |= __GFP_ACCOUNT; > > > > + old_memcg = memalloc_memcg_save(memcg); > > > > + } > > > > > > Please move the get_mem_cgroup_from_page() call out of the > > > declarations and down to right before the if (memcg) branch. > > > > > > > head = NULL; > > > > offset = PAGE_SIZE; > > > > while ((offset -= size) >= 0) { > > > > @@ -835,6 +842,11 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size, > > > > /* Link the buffer to its page */ > > > > set_bh_page(bh, page, offset); > > > > } > > > > +out: > > > > + if (memcg) { > > > > + memalloc_memcg_restore(old_memcg); > > > > +#ifdef CONFIG_MEMCG > > > > + css_put(&memcg->css); > > > > +#endif > > > > > > Please add a put_mem_cgroup() ;) > > > > I've added such helper by commit 8a34a8b7fd62 ("mm, oom: cgroup-aware OOM killer"). > > It's in the mm tree. > > > > I was using mem_cgroup_put() defined by Roman's patch but there were a > lot of build failure reports where someone was taking this series > without Roman's series or applying the series out of order. Andrew > asked me to keep it like this and then he will convert these callsites > into mem_cgroup_put() after making making sure Roman's series is > applied in mm tree. I will recheck with him, how he wants to handle it > now. I can also split the introduction of mem_cgroup_put() into a separate commit, as it seems to be usable not only by the cgroup oom stuff. Please, let me know, if it's a preferred way to go. Thanks!