Messages in this thread | | | Date | Mon, 26 Apr 2021 16:40:21 +0100 | From | Matthew Wilcox <> | Subject | Re: [RFC PATCH] f2fs: restructure f2fs page.private layout |
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On Mon, Apr 26, 2021 at 06:09:08PM +0800, Chao Yu wrote: > Restruct f2fs page private layout for below reasons: > > There are some cases that f2fs wants to set a flag in a page to > indicate a specified status of page: > a) page is in transaction list for atomic write > b) page contains dummy data for aligned write > c) page is migrating for GC > d) page contains inline data for inline inode flush > e) page is verified in merkle tree for fsverity
hm, why do you need to record that? I would have thought that if a file is marked as being protected by the merkle tree then any pages read in would be !uptodate until the merkle tree verification had happened.
> f) page is dirty and has filesystem/inode reference count for writeback > g) page is temporary and has decompress io context reference for compression > > There are existed places in page structure we can use to store > f2fs private status/data: > - page.flags: PG_checked, PG_private > - page.private > > However it was a mess when we using them, which may cause potential > confliction: > page.private PG_private PG_checked > a) -1 set > b) -2 > c), d), e) set > f) 0 set > g) pointer set > > The other problem is page.flags has no free slot, if we can avoid set > zero to page.private and set PG_private flag, then we use non-zero value > to indicate PG_private status, so that we may have chance to reclaim > PG_private slot for other usage. [1] > > So in this patch let's restructure f2fs' page.private as below: > > Layout A: lowest bit should be 1 > | bit0 = 1 | bit1 | bit2 | ... | bit MAX | private data .... | > bit 0 PAGE_PRIVATE_NOT_POINTER > bit 1 PAGE_PRIVATE_ATOMIC_WRITE > bit 2 PAGE_PRIVATE_DUMMY_WRITE > bit 3 PAGE_PRIVATE_ONGOING_MIGRATION > bit 4 PAGE_PRIVATE_INLINE_INODE > bit 5 PAGE_PRIVATE_REF_RESOURCE > bit 6- f2fs private data > > Layout B: lowest bit should be 0 > page.private is a wrapped pointer. > > After the change: > page.private PG_private PG_checked > a) 11 set > b) 101 > c) 1001 > d) 10001 > e) set > f) 100001 set > g) pointer set
Mmm ... this isn't enough to let us remove PG_private. We'd need PG_private to be set for b,c,d as well.
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c > index 817d0bcb5c67..e393a67a023c 100644 > --- a/fs/f2fs/checkpoint.c > +++ b/fs/f2fs/checkpoint.c > @@ -444,7 +444,11 @@ static int f2fs_set_meta_page_dirty(struct page *page) > if (!PageDirty(page)) { > __set_page_dirty_nobuffers(page); > inc_page_count(F2FS_P_SB(page), F2FS_DIRTY_META); > - f2fs_set_page_private(page, 0); > + set_page_private_reference(page); > + if (!PagePrivate(page)) { > + SetPagePrivate(page); > + get_page(page); > + }
I'm not a big fan of this pattern (which seems to be repeated quite often) I think it should be buried within set_page_private_reference(). Also, are the states abcdf all mutually exclusive, or can a page be in states (eg) b and d at the same time?
> - if (IS_DUMMY_WRITTEN_PAGE(page)) { > - set_page_private(page, (unsigned long)NULL); > + if (page_private_dummy(page)) { > + clear_page_private_dummy(page); > ClearPagePrivate(page);
I think the ClearPagePrivate should be buried in the page_private_dummy() macro too ... and shouldn't there be a put_page() for this too?
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