Messages in this thread | | | Subject | Re: [RFC PATCH] f2fs: restructure f2fs page.private layout | From | Chao Yu <> | Date | Tue, 27 Apr 2021 10:32:30 +0800 |
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On 2021/4/26 23:40, Matthew Wilcox wrote: > 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.
I should describe more clearly about the page, the page is belong to merkle tree, rather than the one contains user data, for more details:
https://elixir.bootlin.com/linux/latest/source/fs/verity/verify.c#L69
> >> 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
Sorry,
b) should have set PG_private.
>> 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
ditto,
>> 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.
I can try to add PG_private for c) and d).
> >> 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,
Let me check how to avoid duplicated codes.
> are the states abcdf all mutually exclusive, or can a page be in states > (eg) b and d at the same time?
Not all states are mutually exclusive, e.g a) and f) are mutually exclusive.
> >> - 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?
b) and g) are allocated from mempool, should we add one extra reference count for them after set PG_private?
Thanks,
> > . >
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