On 13:43 Срд 13 Июн , Nick Piggin wrote: > On Wed, Jun 13, 2007 at 05:40:05PM +0400, Dmitriy Monakhov wrote: > > On 14:19 ?????? 29 ?????? , akpm@xxxxxxxxxxxxxxxxxxxx wrote: > > > > > > The patch titled > > > fs: introduce write_begin, write_end, and perform_write aops > > > has been added to the -mm tree. Its filename is > > > fs-introduce-write_begin-write_end-and-perform_write-aops.patch > > > > > > *** Remember to use Documentation/SubmitChecklist when testing your code *** > > > > > > See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find > > > out what to do about this > > > > > > ------------------------------------------------------ > > > Subject: fs: introduce write_begin, write_end, and perform_write aops > > > From: Nick Piggin <npiggin@xxxxxxx> > > > > > > These are intended to replace prepare_writ eand commit_write with more > > > flexible alternatives that are also able to avoid the buffered write > > > deadlock problems efficiently (which prepare_write is unable to do). > > > > > > [mark.fasheh@xxxxxxxxxx: API design contributions, code review and fixes] > > > Signed-off-by: Nick Piggin <npiggin@xxxxxxx> > > > Signed-off-by: Mark Fasheh <mark.fasheh@xxxxxxxxxx> > > > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > I've finaly find time to review Nick's "write_begin/write_end aop" patch set. > > And i have some fixes and questions. My be i've missed somthing and it was > > already disscussed, but i cant find in LKML. > > Thanks, that's really helpful. > > > > 1) loop dev: > > loop.c code itself is not perfect. In fact before Nick's patch > > partial write was't possible. Assumption what write chunks are > > always page aligned is realy weird ( see "index++" line). > > Fixed by "new aop loop fix" patch > > I think you're right, fix looks good. > > > > 2)block_write_begin: > > After we enter to block_write_begin with *pagep == NULL and > > some page was grabed we remember this page in *pagep > > And if __block_prepare_write() we have to clear *pagep , as > > it was before. Because this may confuse caller. > > for example caller may have folowing code: > > ret = block_write_begin(..., pagep,...) > > if (ret && *pagep != NULL) { > > unlock_page(*pagep); > > page_cache_release(*pagep); > > } > > Fixed my "new aop block_write_begin fix" patch > > I don't think the caller can rely on that if it returns failure. > But that is more defensive I guess. Maybe setting it to 1 or > so would catch abusers. > > > > 3) __page_symlink: > > Nick's patch add folowing code: > > + err = pagecache_write_begin(NULL, mapping, 0,PAGE_CACHE_SIZE, > > + AOP_FLAG_UNINTERRUPTIBLE, &page,&fsdata); > > symlink now consume whole page. I have only one question "WHY???". > > I don't see any advantages, but where are huge list of > > dissdvantages: > > a) fs with blksize == 1k and pagesize == 16k after this patch > > waste more than 10x times disk space for nothing. > > b) What happends if we want use fs with blksize == 4k on i386 > > after it was used by ia64 ??? (before this patch it was > > possible). One more visiable effect caused by wrong symlink size: fsstress cause folowing error: <LOG BEGIN> EXT3-fs unexpected failure: !buffer_revoked(bh); inconsistent data on disk ext3_forget: aborting transaction: IO failure in __ext3_journal_revoke ext3_abort called. EXT3-fs error (device dm-4): ext3_forget: error -5 when attempting revoke Remounting filesystem read-only Aborting journal on device dm-4. journal commit I/O error journal commit I/O error journal commit I/O error journal commit I/O error journal commit I/O error journal commit I/O error EXT3-fs error (device dm-4) in ext3_free_blocks_sb: Journal has aborted journal commit I/O error journal commit I/O error EXT3-fs error (device dm-4) in ext3_reserve_inode_write: Journal has aborted EXT3-fs error (device dm-4) in ext3_truncate: IO failure journal commit I/O error journal commit I/O error journal commit I/O error journal commit I/O error EXT3-fs error (device dm-4) in ext3_reserve_inode_write: Journal has aborted EXT3-fs error (device dm-4) in ext3_orphan_del: Journal has aborted EXT3-fs error (device dm-4) in ext3_reserve_inode_write: Journal has aborted EXT3-fs error (device dm-4) in ext3_delete_inode: IO failure <LOG END> After symlink size was fixed to len-1 problem dissappeared. > > > > I dont prepare patch for this because i dont understand issue > > witch Nick aimed to fix. > > I don't know why myself :P I think it would be just fine to use > len-1 as it did previously, so it must have been a typo? > > > > 4) iov_iter_fault_in_readable: > > Function prerform check for signgle region, with out respect to > > segment nature of iovec, For example writev no longer works :) : > > writev(3, [{"\1", 1}, {"\2"..., 4096}], 2) = -1 EFAULT (Bad address) > > this hidden bug, and it was invisiable because XXXX_fault_in_readable > > return value was ignored before. Lets iov_iter_fault_in_readable > > perform checks for all segments. > > Fixed by :"iov_iter_fault_in_readable fix" > > OK thanks. I would rather just change this to use the length of > the first iovec always (prefaulting multiple iovecs would have to > be benchmarked on real apps that make heavy use of writev, I > suspect). > > > > 5) ext3_write_end: > > Before write_begin/write_end patch set we have folowing locking > > order: > > stop_journal(handle); > > unlock_page(page); > > But now order is oposite: > > unlock_page(page); > > stop_journal(handle); > > Can we got any race condition now? I'm not sure is it actual problem, > > may be somebody cant describe this. > > Can we just change it to the original order? That would seem to be > safest unless one of the ext3 devs explicitly acks it. > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
