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Date: Tue, 18 Jan 2011 16:41:33 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: Daisuke Nishimura <nishimura@....nes.nec.co.jp> Cc: Miklos Szeredi <miklos@...redi.hu>, minchan.kim@...il.com, kamezawa.hiroyu@...fujitsu.com, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v4] mm: add replace_page_cache_page() function On Wed, 19 Jan 2011 09:27:33 +0900 Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote: > On Tue, 18 Jan 2011 15:28:44 -0800 > Andrew Morton <akpm@...ux-foundation.org> wrote: > > > On Tue, 18 Jan 2011 12:18:11 +0100 > > Miklos Szeredi <miklos@...redi.hu> wrote: > > > > > +int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask) > > > +{ > > > + int error; > > > + struct mem_cgroup *memcg = NULL; > > > > I'm suspecting that the unneeded initialisation was added to suppress a > > warning? > > > No. > It's necessary for mem_cgroup_{prepare|end}_migration(). > mem_cgroup_prepare_migration() will return without doing anything in > "if (mem_cgroup_disabled()" case(iow, "memcg" is not overwritten), > but mem_cgroup_end_migration() depends on the value of "memcg" to decide > whether prepare_migration has succeeded or not. > This may not be a good implementation, It's a *surprising* implementation, in the context of kernel conventions. At least, it fooled me :) Which makes it a not-good implementation, really. Also, it's undocumented. > but IMHO I'd like to to initialize > valuable before using it in general. mem_cgroup_prepare_migration() performs the initialisation! We do this in many places - it's the basic "function with more than one return value" mechanism. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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