| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-Id: <E1JbWvF-0005Hr-Ur@pomaz-ex.szeredi.hu>
Date: Tue, 18 Mar 2008 09:11:49 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: akpm@...ux-foundation.org
CC: a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch 4/8] mm: allow not updating BDI stats in
end_page_writeback()
[PeterZ added to CC]
> On Mon, 17 Mar 2008 20:19:12 +0100 Miklos Szeredi <miklos@...redi.hu> wrote:
>
> > From: Miklos Szeredi <mszeredi@...e.cz>
> >
> > Fuse's writepage will need to clear page writeback separately from
> > updating the per BDI counters.
> >
> > This patch renames end_page_writeback() to __end_page_writeback() and
> > adds a boolean parameter to indicate if the per BDI stats need to be
> > updated.
> >
> > Regular callers get an inline end_page_writeback() without the boolean
> > parameter.
> >
> > ...
> >
> > Index: linux/include/linux/page-flags.h
> > ===================================================================
> > --- linux.orig/include/linux/page-flags.h 2008-03-17 18:24:13.000000000 +0100
> > +++ linux/include/linux/page-flags.h 2008-03-17 18:25:53.000000000 +0100
> > @@ -300,7 +300,7 @@ struct page; /* forward declaration */
> >
> > extern void cancel_dirty_page(struct page *page, unsigned int account_size);
> >
> > -int test_clear_page_writeback(struct page *page);
> > +int test_clear_page_writeback(struct page *page, bool bdi_stats);
> > int test_set_page_writeback(struct page *page);
> >
> > static inline void set_page_writeback(struct page *page)
> > Index: linux/include/linux/pagemap.h
> > ===================================================================
> > --- linux.orig/include/linux/pagemap.h 2008-03-17 18:24:13.000000000 +0100
> > +++ linux/include/linux/pagemap.h 2008-03-17 18:25:53.000000000 +0100
> > @@ -223,7 +223,12 @@ static inline void wait_on_page_writebac
> > wait_on_page_bit(page, PG_writeback);
> > }
> >
> > -extern void end_page_writeback(struct page *page);
> > +extern void __end_page_writeback(struct page *page, bool bdi_stats);
> > +
> > +static inline void end_page_writeback(struct page *page)
> > +{
> > + __end_page_writeback(page, true);
> > +}
> >
> > /*
> > * Fault a userspace page into pagetables. Return non-zero on a fault.
> > Index: linux/mm/filemap.c
> > ===================================================================
> > --- linux.orig/mm/filemap.c 2008-03-17 18:25:38.000000000 +0100
> > +++ linux/mm/filemap.c 2008-03-17 18:25:53.000000000 +0100
> > @@ -574,19 +574,20 @@ EXPORT_SYMBOL(unlock_page);
> > /**
> > * end_page_writeback - end writeback against a page
> > * @page: the page
> > + * @bdi_stats: update the per-bdi writeback counter
> > */
> > -void end_page_writeback(struct page *page)
> > +void __end_page_writeback(struct page *page, bool bdi_stats)
> > {
> > if (TestClearPageReclaim(page))
> > rotate_reclaimable_page(page);
> >
> > - if (!test_clear_page_writeback(page))
> > + if (!test_clear_page_writeback(page, bdi_stats))
> > BUG();
> >
> > smp_mb__after_clear_bit();
> > wake_up_page(page, PG_writeback);
> > }
> > -EXPORT_SYMBOL(end_page_writeback);
> > +EXPORT_SYMBOL(__end_page_writeback);
> >
> > /**
> > * __lock_page - get a lock on the page, assuming we need to sleep to get it
> > Index: linux/mm/page-writeback.c
> > ===================================================================
> > --- linux.orig/mm/page-writeback.c 2008-03-17 18:25:17.000000000 +0100
> > +++ linux/mm/page-writeback.c 2008-03-17 18:25:53.000000000 +0100
> > @@ -1242,7 +1242,7 @@ int clear_page_dirty_for_io(struct page
> > }
> > EXPORT_SYMBOL(clear_page_dirty_for_io);
> >
> > -int test_clear_page_writeback(struct page *page)
> > +int test_clear_page_writeback(struct page *page, bool bdi_stats)
> > {
> > struct address_space *mapping = page_mapping(page);
> > int ret;
> > @@ -1257,7 +1257,7 @@ int test_clear_page_writeback(struct pag
> > radix_tree_tag_clear(&mapping->page_tree,
> > page_index(page),
> > PAGECACHE_TAG_WRITEBACK);
> > - if (bdi_cap_writeback_dirty(bdi)) {
> > + if (bdi_stats && bdi_cap_writeback_dirty(bdi)) {
> > __dec_bdi_stat(bdi, BDI_WRITEBACK);
> > __bdi_writeout_inc(bdi);
> > }
>
> Adding `mode' flags to a core function is generally considered poor form.
> And it adds additional overhead and possibly stack utilisation for all
> callers.
>
> We generally prefer that a new function be created. After all, that's what
> you've done here, only the code has gone and wedged two different functions
> into one.
Yes, although duplicating such a not entirely trivial function has
it's dangers as well, I think.
> Another approach might be to add a new bdi_cap_foo() flag. We could then do
>
> if (bdi_cap_writeback_dirty(bdi) && bdi_cap_mumble(bdi)) {
>
> here. But even better would be to create a new BDI capability which
> indicates that this address_space doesn't want this treatment in
> test_clear_page_writeback(), then go fix up all the
> !bdi_cap_writeback_dirty() address_spaces to set that flag.
>
> So then the code becomes
>
> if (!bdi_cap_account_writeback_in_test_clear_page_writeback(bdi)) {
>
> (good luck thinking up a better name ;))
>
> Reason: bdi_cap_writeback_dirty() is kinda weirdly intrepreted to mean
> various different things in different places and we really should separate
> its multiple interpretations into separate flags.
>
> Note that this becomes a standalone VFS cleanup patch, and the fuse code
> can then just use it later on.
Hmm, I can see two slightly different meanings of bdi_cap_writeback_dirty():
1) need to call ->writepage (sync_page_range(), ...)
2) need to update BDI stats (test_clear_page_writeback(), ...)
If these two were different flags, then fuse could set the
NEED_WRITEPAGE flag, but clear the NEED_UPDATE_BDI_STATS flag, and do
it manually.
Does that sound workable?
Thanks,
Miklos
--
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/
Powered by blists - more mailing lists